diff --git a/bot/world/chunk.go b/bot/world/chunk.go
index 2d2a97a..36fc3a1 100644
--- a/bot/world/chunk.go
+++ b/bot/world/chunk.go
@@ -3,94 +3,167 @@ package world
 import (
 	"bytes"
 	"fmt"
-	// "io"
 	"github.com/Tnze/go-mc/data"
 	pk "github.com/Tnze/go-mc/net/packet"
+	"math"
 )
 
-//DecodeChunkColumn decode the chunk data structure
+// DecodeChunkColumn decode the chunk data structure.
+// If decoding went error, successful decoded data will be returned.
 func DecodeChunkColumn(mask int32, data []byte) (*Chunk, error) {
 	var c Chunk
 	r := bytes.NewReader(data)
 	for sectionY := 0; sectionY < 16; sectionY++ {
-		if (mask & (1 << uint(sectionY))) == 0 { // Is the given bit set in the mask?
-			continue
-		}
-		var (
-			BlockCount   pk.Short
-			BitsPerBlock pk.Byte
-		)
-		if err := BlockCount.Decode(r); err != nil {
-			return nil, err
-		}
-		if err := BitsPerBlock.Decode(r); err != nil {
-			return nil, err
-		}
-		//读调色板
-		var palette []uint
-		if BitsPerBlock < 9 {
-			var length pk.VarInt
-			if err := length.Decode(r); err != nil {
-				return nil, fmt.Errorf("read palette (id len) fail: %v", err)
-			}
-			palette = make([]uint, length)
-
-			for id := uint(0); id < uint(length); id++ {
-				var stateID pk.VarInt
-				if err := stateID.Decode(r); err != nil {
-					return nil, fmt.Errorf("read palette (id) fail: %v", err)
-				}
-
-				palette[id] = uint(stateID)
+		// If the section's bit set in the mask
+		if (mask & (1 << uint(sectionY))) != 0 {
+			// read section
+			sec, err := readSection(r)
+			if err != nil {
+				return &c, fmt.Errorf("read section[%d] error: %w", sectionY, err)
 			}
+			c.Sections[sectionY] = sec
 		}
-
-		//Section数据
-		var DataArrayLength pk.VarInt
-		if err := DataArrayLength.Decode(r); err != nil {
-			return nil, fmt.Errorf("read DataArrayLength fail: %v", err)
-		}
-
-		DataArray := make([]int64, DataArrayLength)
-		for i := 0; i < int(DataArrayLength); i++ {
-			if err := (*pk.Long)(&DataArray[i]).Decode(r); err != nil {
-				return nil, fmt.Errorf("read DataArray fail: %v", err)
-			}
-		}
-		//用数据填充区块
-		fillSection(&c.sections[sectionY], perBits(byte(BitsPerBlock)), DataArray, palette)
 	}
-
 	return &c, nil
 }
 
-func perBits(BitsPerBlock byte) uint {
+func perBits(BitsPerBlock byte) int {
 	switch {
 	case BitsPerBlock <= 4:
 		return 4
 	case BitsPerBlock < 9:
-		return uint(BitsPerBlock)
+		return int(BitsPerBlock)
 	default:
-		return uint(data.BitsPerBlock) // DefaultBitsPerBlock
+		return data.BitsPerBlock // DefaultBitsPerBlock
 	}
 }
 
-func fillSection(s *Section, bpb uint, DataArray []int64, palette []uint) {
-	mask := uint(1<<bpb - 1)
-	for n := 0; n < 16*16*16; n++ {
-		offset := uint(n * int(bpb))
-		data := uint(DataArray[offset/64])
-		data >>= offset % 64
-		if offset%64 > 64-bpb {
-			l := 64 - offset % 64
-			data |= uint(DataArray[offset/64+1] << l)
+func readSection(data pk.DecodeReader) (s Section, err error) {
+	var BlockCount pk.Short
+	if err := BlockCount.Decode(data); err != nil {
+		return nil, fmt.Errorf("read block count error: %w", err)
+	}
+	var bpb pk.UnsignedByte
+	if err := bpb.Decode(data); err != nil {
+		return nil, fmt.Errorf("read bits per block error: %w", err)
+	}
+	// If bpb values greater than or equal to 9, use directSection.
+	// Otherwise use paletteSection.
+	var palettes []BlockStatus
+	var palettesIndex map[BlockStatus]int
+	if bpb < 9 {
+		// read palettes
+		var length pk.VarInt
+		if err := length.Decode(data); err != nil {
+			return nil, fmt.Errorf("read palettes length error: %w", err)
 		}
-		data &= mask
-
-		if bpb < 9 {
-			s.blocks[n%16][n/(16*16)][n%(16*16)/16].id = palette[data]
-		} else {
-			s.blocks[n%16][n/(16*16)][n%(16*16)/16].id = data
+		palettes = make([]BlockStatus, length)
+		palettesIndex = make(map[BlockStatus]int, length)
+		for i := 0; i < int(length); i++ {
+			var v pk.VarInt
+			if err := v.Decode(data); err != nil {
+				return nil, fmt.Errorf("read palettes[%d] error: %w", i, err)
+			}
+			palettes[i] = BlockStatus(v)
+			palettesIndex[BlockStatus(v)] = i
 		}
 	}
+
+	// read data array
+	var dataLen pk.VarInt
+	if err := dataLen.Decode(data); err != nil {
+		return nil, fmt.Errorf("read data array length error: %w", err)
+	}
+	if int(dataLen) < 16*16*16*int(bpb)/64 {
+		return nil, fmt.Errorf("data length (%d) is not enough of given bpb (%d)", dataLen, bpb)
+	}
+	dataArray := make([]uint64, dataLen)
+	for i := 0; i < int(dataLen); i++ {
+		var v pk.Long
+		if err := v.Decode(data); err != nil {
+			return nil, fmt.Errorf("read dataArray[%d] error: %w", i, err)
+		}
+		dataArray[i] = uint64(v)
+	}
+
+	sec := directSection{bpb: perBits(byte(bpb)), data: dataArray}
+	if bpb < 9 {
+		return &paletteSection{
+			palette:       palettes,
+			palettesIndex: palettesIndex,
+			directSection: sec,
+		}, nil
+	} else {
+		return &sec, nil
+	}
+}
+
+type directSection struct {
+	bpb  int
+	data []uint64
+}
+
+func (d *directSection) GetBlock(offset int) BlockStatus {
+	offset *= d.bpb
+	padding := offset % 64
+	block := uint32(d.data[offset/64] >> padding)
+	if padding > 64-d.bpb {
+		l := 64 - padding
+		block |= uint32(d.data[offset/64+1] << l)
+	}
+	return BlockStatus(block & (1<<d.bpb - 1)) // mask
+}
+
+func (d *directSection) SetBlock(offset int, s BlockStatus) {
+	offset *= d.bpb
+	padding := offset % 64
+	mask := uint64(math.MaxUint64<<(padding+d.bpb) | (1<<padding - 1))
+	d.data[offset/64] = d.data[offset/64]&mask | uint64(s)<<padding
+	if padding > 64-d.bpb {
+		l := padding - (64 - d.bpb)
+		d.data[offset/64+1] = d.data[offset/64+1]&(math.MaxUint64<<l) | uint64(s)>>(64-padding)
+	}
+}
+
+func (d *directSection) CanContain(s BlockStatus) bool {
+	return s <= (1<<d.bpb - 1)
+}
+
+func (d *directSection) clone(bpb int) *directSection {
+	newSection := &directSection{
+		bpb:  bpb,
+		data: make([]uint64, 16*16*16*bpb/64),
+	}
+	for offset := 0; offset < 16*16*16; offset++ {
+		newSection.SetBlock(offset, d.GetBlock(offset))
+	}
+	return newSection
+}
+
+type paletteSection struct {
+	palette       []BlockStatus
+	palettesIndex map[BlockStatus]int
+	directSection
+}
+
+func (p *paletteSection) GetBlock(offset int) BlockStatus {
+	v := p.directSection.GetBlock(offset)
+	return p.palette[v]
+}
+
+func (p *paletteSection) SetBlock(offset int, s BlockStatus) {
+	if i, ok := p.palettesIndex[s]; ok {
+		p.directSection.SetBlock(offset, BlockStatus(i))
+		return
+	}
+	i := len(p.palette)
+	p.palette = append(p.palette, s)
+	p.palettesIndex[s] = i
+	if !p.directSection.CanContain(BlockStatus(i)) {
+		// Increase the underlying directSection
+		// Suppose that old bpb fit len(p.palette) before it appended.
+		// So bpb+1 must enough for new len(p.palette).
+		p.directSection = *p.directSection.clone(p.bpb + 1)
+	}
+	p.directSection.SetBlock(offset, BlockStatus(i))
 }
diff --git a/bot/world/chunk_test.go b/bot/world/chunk_test.go
new file mode 100644
index 0000000..13b5fda
--- /dev/null
+++ b/bot/world/chunk_test.go
@@ -0,0 +1,78 @@
+package world
+
+import (
+	"github.com/Tnze/go-mc/data"
+	"math/rand"
+	"testing"
+)
+
+func newDirectSection(bpb int) Section {
+	return &directSection{
+		bpb:  bpb,
+		data: make([]uint64, 16*16*16*bpb/64),
+	}
+}
+
+func TestDirectSection(t *testing.T) {
+	for bpb := 4; bpb <= data.BitsPerBlock; bpb++ {
+		testSection(newDirectSection(bpb), bpb)(t)
+	}
+}
+
+func TestDirectSection_clone(t *testing.T) {
+	s := newDirectSection(9)
+	dataset := randData(9)
+	for i := 0; i < 16*16*16; i++ {
+		s.SetBlock(i, dataset[i])
+	}
+	s = s.(*directSection).clone(data.BitsPerBlock)
+	for i := 0; i < 16*16*16; i++ {
+		if s := s.GetBlock(i); dataset[i] != s {
+			t.Fatalf("direct section error: want: %v, get %v", dataset[i], s)
+		}
+	}
+}
+
+func TestPaletteSection(t *testing.T) {
+	t.Run("Correctness", testSection(&paletteSection{
+		palettesIndex: make(map[BlockStatus]int),
+		directSection: *(newDirectSection(7).(*directSection)),
+	}, 7))
+	t.Run("AutomaticExpansion", testSection(&paletteSection{
+		palettesIndex: make(map[BlockStatus]int),
+		directSection: *(newDirectSection(4).(*directSection)),
+	}, 9))
+}
+
+func testSection(s Section, bpb int) func(t *testing.T) {
+	return func(t *testing.T) {
+		for _, dataset := range [][16 * 16 * 16]BlockStatus{secData(bpb), randData(bpb)} {
+			for i := 0; i < 16*16*16; i++ {
+				s.SetBlock(i, dataset[i])
+			}
+			for i := 0; i < 16*16*16; i++ {
+				if v := s.GetBlock(i); dataset[i] != v {
+					t.Fatalf("direct section error: want: %v, get %v", dataset[i], v)
+				}
+			}
+		}
+	}
+}
+
+func secData(bpb int) (data [16 * 16 * 16]BlockStatus) {
+	mask := 1<<bpb - 1
+	var v int
+	for i := range data {
+		data[i] = BlockStatus(v)
+		v = (v + 1) & mask
+	}
+	return
+}
+
+func randData(bpb int) (data [16 * 16 * 16]BlockStatus) {
+	data = secData(bpb)
+	rand.Shuffle(len(data), func(i, j int) {
+		data[i], data[j] = data[j], data[i]
+	})
+	return
+}
diff --git a/bot/world/motion.go b/bot/world/motion.go
deleted file mode 100644
index acfa17c..0000000
--- a/bot/world/motion.go
+++ /dev/null
@@ -1,78 +0,0 @@
-package world
-
-// import (
-// 	"math"
-// 	"time"
-// )
-
-// // SetPosition method move your character around.
-// // Server will ignore this if changes too much.
-// func (g *Client) SetPosition(x, y, z float64, onGround bool) {
-// 	g.motion <- func() {
-// 		g.player.X, g.player.Y, g.player.Z = x, y, z
-// 		g.player.OnGround = onGround
-// 		sendPlayerPositionPacket(g) //向服务器更新位置
-// 	}
-// }
-
-// // LookAt method turn player's hand and make it look at a point.
-// func (g *Client) LookAt(x, y, z float64) {
-// 	x0, y0, z0 := g.player.X, g.player.Y, g.player.Z
-// 	x, y, z = x-x0, y-y0, z-z0
-
-// 	r := math.Sqrt(x*x + y*y + z*z)
-// 	yaw := -math.Atan2(x, z) / math.Pi * 180
-// 	for yaw < 0 {
-// 		yaw = 360 + yaw
-// 	}
-// 	pitch := -math.Asin(y/r) / math.Pi * 180
-
-// 	g.LookYawPitch(float32(yaw), float32(pitch))
-// }
-
-// // LookYawPitch set player's hand to the direct by yaw and pitch.
-// // yaw can be [0, 360) and pitch can be (-180, 180).
-// // if |pitch|>90 the player's hand will be very strange.
-// func (g *Client) LookYawPitch(yaw, pitch float32) {
-// 	g.motion <- func() {
-// 		g.player.Yaw, g.player.Pitch = yaw, pitch
-// 		sendPlayerLookPacket(g) //向服务器更新朝向
-// 	}
-// }
-
-// // SwingHand sent when the player's arm swings.
-// // if hand is true, swing the main hand
-// func (g *Client) SwingHand(hand bool) {
-// 	if hand {
-// 		sendAnimationPacket(g, 0)
-// 	} else {
-// 		sendAnimationPacket(g, 1)
-// 	}
-// }
-
-// // Dig a block in the position and wait for it's breaked
-// func (g *Client) Dig(x, y, z int) error {
-// 	b := g.GetBlock(x, y, z).id
-// 	sendPlayerDiggingPacket(g, 0, x, y, z, Top) //start
-// 	sendPlayerDiggingPacket(g, 2, x, y, z, Top) //end
-
-// 	for {
-// 		time.Sleep(time.Millisecond * 50)
-// 		if g.GetBlock(x, y, z).id != b {
-// 			break
-// 		}
-// 		g.SwingHand(true)
-// 	}
-
-// 	return nil
-// }
-
-// // UseItem use the item in hand.
-// // if hand is true, swing the main hand
-// func (g *Client) UseItem(hand bool) {
-// 	if hand {
-// 		sendUseItemPacket(g, 0)
-// 	} else {
-// 		sendUseItemPacket(g, 1)
-// 	}
-// }
diff --git a/bot/world/world.go b/bot/world/world.go
index 975bec6..58a7e89 100644
--- a/bot/world/world.go
+++ b/bot/world/world.go
@@ -4,27 +4,34 @@ import (
 	"github.com/Tnze/go-mc/bot/world/entity"
 )
 
-//World record all of the things in the world where player at
+// World record all of the things in the world where player at
 type World struct {
 	Entities map[int32]entity.Entity
 	Chunks   map[ChunkLoc]*Chunk
 }
 
-//Chunk store a 256*16*16 clolumn blocks
+// Chunk store a 256*16*16 column blocks
 type Chunk struct {
-	sections [16]Section
+	Sections [16]Section
 }
 
-//Section store a 16*16*16 cube blocks
-type Section struct {
-	blocks [16][16][16]Block
+// Section store a 16*16*16 cube blocks
+type Section interface {
+	// GetBlock return block status, offset can be calculate by SectionOffset.
+	GetBlock(offset int) BlockStatus
+	// SetBlock is the reverse operation of GetBlock.
+	SetBlock(offset int, s BlockStatus)
 }
 
-//Block is the base of world
-type Block struct {
-	id uint
+func SectionOffset(x, y, z int) (offset int) {
+	// According to wiki.vg: Data Array is given for each block with increasing x coordinates,
+	// within rows of increasing z coordinates, within layers of increasing y coordinates.
+	// So offset equals to ( x*16^0 + z*16^1 + y*16^2 )*(bits per block).
+	return x + z*16 + y*16*16
 }
 
+type BlockStatus uint32
+
 type ChunkLoc struct {
 	X, Z int
 }
@@ -47,25 +54,18 @@ type ChunkLoc struct {
 // 	East
 // )
 
-// // getBlock return the block in the position (x, y, z)
-// func (w *world) getBlock(x, y, z int) Block {
-// 	c := w.chunks[chunkLoc{x >> 4, z >> 4}]
-// 	if c != nil {
-// 		cx, cy, cz := x&15, y&15, z&15
-// 		/*
-// 			n = n&(16-1)
-
-// 			is equal to
-
-// 			n %= 16
-// 			if n < 0 { n += 16 }
-// 		*/
-
-// 		return c.sections[y/16].blocks[cx][cy][cz]
-// 	}
-
-// 	return Block{id: 0}
-// }
+// getBlock return the block in the position (x, y, z)
+func (w *World) GetBlockStatus(x, y, z int) BlockStatus {
+	// Use n>>4 rather then n/16. It acts wrong if n<0.
+	c := w.Chunks[ChunkLoc{x >> 4, z >> 4}]
+	if c != nil {
+		// (n&(16-1)) == (n<0 ? n%16+16 : n%16)
+		if sec := c.Sections[y>>4]; sec != nil {
+			return sec.GetBlock(SectionOffset(x&15, y&15, z&15))
+		}
+	}
+	return 0
+}
 
 // func (b Block) String() string {
 // 	return blockNameByID[b.id]
diff --git a/bot/world/world_test.go b/bot/world/world_test.go
deleted file mode 100644
index 641e28b..0000000
--- a/bot/world/world_test.go
+++ /dev/null
@@ -1,9 +0,0 @@
-package world
-
-// import "testing"
-
-// func TestBlockString(t *testing.T) {
-// 	for i := uint(0); i < 8598+1; i++ {
-// 		t.Log(Block{id: i})
-// 	}
-// }