diff --git a/db.go b/db.go
index 2cbc349..38fabe2 100644
--- a/db.go
+++ b/db.go
@@ -15,13 +15,12 @@ import (
 	"github.com/sirupsen/logrus"
 	"io/ioutil"
 	"os"
-	"sort"
 	"time"
 )
 
 type DB struct {
-	memory *Engine
-	wal    *os.File
+	memDB *MemDB
+	wal   *os.File
 
 	dir string
 	walPath string
@@ -43,7 +42,7 @@ func Open(dirPath string) (*DB, error) {
 	}
 	wal = wa
 
-	db := &DB{memory: NewEngine(), wal: wal, dir: dirPath, walPath: walPath}
+	db := &DB{memDB: NewEngine(), wal: wal, dir: dirPath, walPath: walPath}
 	err = db.recoveryDB()
 	if err != nil {
 		logrus.Error(err)
@@ -97,7 +96,7 @@ func (db *DB) Close() {
 }
 
 func (db *DB) Get(key string) (Value, error) {
-	value, err := db.memory.Get(key)
+	value, err := db.memDB.Get(key)
 	// 如果没有得到value
 	if err == nil {
 		return value, err
@@ -114,15 +113,15 @@ func (db *DB) Put(key, value string) error {
 func (db *DB) put(kv KeyValue) error {
 	// TODO: 改进写日志的方式
 	db.writeAheadLog(kv)
-	db.memory.Put(kv)
+	db.memDB.Put(kv)
 	// 这个阈值用常量 MaxMemSize表示, MaxMemSize定义在配置文件中, 后续改为可配置的量
-	if db.memory.memSize >= config.MaxMemSize {
+	if db.memDB.memSize >= config.MaxMemSize {
 		// 刷到磁盘
 		db.flush()
 		// TODO: 之后实现异步的flush操作
-		db.memory.memStore = make(map[string]Value)
+		db.memDB.memStore = NewSkipList()
 		// ! 这个也要重置
-		db.memory.memSize = 0
+		db.memDB.memSize = 0
 		// 清空 wal.log 文件内容, 用直接创建的方式
 		// Create creates or truncates the named file. If the file already exists, it is truncated.
 		wal, err := os.Create(db.walPath)
@@ -140,14 +139,15 @@ func (db *DB) put(kv KeyValue) error {
 func (db *DB) Delete(key string) error {
 	delTime := time.Now().UnixNano() / 1e6
 	db.writeAheadLog(KeyValue{Key: key, Val: Value{"", delTime, DEL}})
-	return db.memory.Delete(key, delTime)
+	return db.memDB.Delete(key, delTime)
 }
 
+// 暂时不需要区间扫描
 // 扫描一个区间的key, 得到key value的结果slice
 // 如果value为deleted, 那么不添加
-func (db *DB) Scan(startKey, endKey string) ([]KeyValue, error) {
-	return db.memory.Scan(startKey, endKey)
-}
+//func (db *DB) Scan(startKey, endKey string) ([]KeyValue, error) {
+//	return db.memDB.Scan(startKey, endKey)
+//}
 
 func (db *DB) writeAheadLog(kv KeyValue) error {
 	write := bufio.NewWriter(db.wal)
@@ -172,20 +172,13 @@ func (db *DB) flush() error {
 
 	fileBytes := make([]byte, 0)
 
-	// 有序地flush
-	keys := make([]string, 0, len(db.memory.memStore))
-	for key, _ := range db.memory.memStore {
-		if key == "" {
-			continue
+	// 使用迭代器, 有序(从小到大)地编码
+	it := db.memDB.memStore.NewIterator()
+	for {
+		kv, ok := it.Next()
+		if !ok {
+			break
 		}
-		keys = append(keys, key)
-	}
-	sort.Strings(keys)
-
-	for _, key := range keys {
-		// 编码, [varint_key, key, varint_value, value, Timestamp, Op]
-		kv := KeyValue{Key: key, Val: db.memory.memStore[key]}
-		//logrus.Info(kv.Key)
 		kvBytes := kv.Encode()
 		fileBytes = append(fileBytes, kvBytes...)
 	}
diff --git a/engine.go b/memdb.go
similarity index 70%
rename from engine.go
rename to memdb.go
index 3340028..4592d06 100644
--- a/engine.go
+++ b/memdb.go
@@ -1,12 +1,8 @@
 package gokv
 
-import (
-	"sort"
-)
-
-// the memory Engine
-type Engine struct {
-	memStore map[string]Value
+// the memDB MemDB
+type MemDB struct {
+	memStore *SkipList
 	memSize int  // 记录mem存储的容量, put和del的时候进行计算
 }
 
@@ -92,33 +88,34 @@ func VarIntDecode(bytes []byte) (int, []byte) {
 	return val, bytes[i + 1:]
 }
 
-func NewEngine() *Engine {
-	return &Engine{memStore: make(map[string]Value), memSize: 0}
+func NewEngine() *MemDB {
+	return &MemDB{memStore: NewSkipList(), memSize: 0}
 }
 
-func (e *Engine) Get(key string) (Value, error) {
-	m, ok := e.memStore[key]
+func (e *MemDB) Get(key string) (Value, error) {
+	m, ok := e.memStore.Get(key)
 	if !ok {
 		return Value{}, GetEmptyError
 	}
-	return m, nil
+	return m.Val, nil
 }
 
 // 这个Put只是在内存上的操作, 不涉及磁盘的操作.
-func (e *Engine) Put(kv KeyValue) error {
-	e.memStore[kv.Key] = kv.Val
+func (e *MemDB) Put(kv KeyValue) error {
+	e.memStore.Put(KeyValue{Key: kv.Key, Val: kv.Val})
 	// TODO: 需要调整一下, 加上8字节的时间戳和1字节的Op
 	e.memSize += len(kv.Key) + len(kv.Val.Value) + 8 + 1
 	return nil
 }
 
 // 删除的元素的value用特殊的字符串来代替
-func (e *Engine) Delete(key string, delTime int64) error {
-	val, ok := e.memStore[key]
+func (e *MemDB) Delete(key string, delTime int64) error {
+	kv, ok := e.memStore.Get(key)
+	val := kv.Val
 	if ok {
 		// 这里调整大小只需要调整字符串的大小
 		e.memSize = e.memSize - len(val.Value) + len(deleted)
-		e.memStore[key] = Value{Value: deleted, Timestamp: delTime, Op: DEL}
+		e.memStore.Put(KeyValue{Key: key, Val: Value{Value: deleted, Timestamp: delTime, Op: DEL}})
 	} else {
 		err := e.Put(KeyValue{
 			Key: key,
@@ -133,31 +130,32 @@ func (e *Engine) Delete(key string, delTime int64) error {
 	return nil
 }
 
+// 先注释掉, 这部分暂时不需要
 // 扫描一个区间的key, 得到key value的结果slice
 // 如果value为deleted, 那么不添加
-func (e *Engine) Scan(startKey, endKey string) ([]KeyValue, error) {
-	keys := make([]string, len(e.memStore))
-	i := 0
-	for k := range e.memStore {
-		keys[i] = k
-		i += 1
-	}
-	// 排序
-	sort.Slice(keys, func(i, j int) bool {
-		return keys[i] < keys[j]
-	})
-	kvs := make([]KeyValue, 0)
-	for _, k := range keys {
-		if k >= startKey && k <= endKey {
-			value := e.memStore[k]
-			if value.Value == deleted {  // 如果已删除
-				continue
-			}
-			kvs = append(kvs, KeyValue{Key: k, Val: value})
-		}
-		if k > endKey {
-			break
-		}
-	}
-	return kvs, nil
-}
\ No newline at end of file
+//func (e *MemDB) Scan(startKey, endKey string) ([]KeyValue, error) {
+//	keys := make([]string, e.memStore.Len())
+//	i := 0
+//	for k := range e.memStore {
+//		keys[i] = k
+//		i += 1
+//	}
+//	// 排序
+//	sort.Slice(keys, func(i, j int) bool {
+//		return keys[i] < keys[j]
+//	})
+//	kvs := make([]KeyValue, 0)
+//	for _, k := range keys {
+//		if k >= startKey && k <= endKey {
+//			value := e.memStore[k]
+//			if value.Value == deleted {  // 如果已删除
+//				continue
+//			}
+//			kvs = append(kvs, KeyValue{Key: k, Val: value})
+//		}
+//		if k > endKey {
+//			break
+//		}
+//	}
+//	return kvs, nil
+//}
\ No newline at end of file
diff --git a/readme.md b/readme.md
index 62e5744..201207c 100644
--- a/readme.md
+++ b/readme.md
@@ -33,7 +33,7 @@ A persistent, LSM tree structured key value database engine implemented by go la
 - [x] 实现完整的key-value结构, 包括时间戳
 - [x] 实现基于WAL的故障恢复(启动时从内存恢复)
 - [x] 设计实现varint可变长度编码
-- [ ] SkipList版 Memstore
+- [x] SkipList版 Memstore
 
 
 ## 全部待实现的feature
@@ -46,7 +46,7 @@ A persistent, LSM tree structured key value database engine implemented by go la
 - [x] 实现WAL存储 (暂不实现故障恢复功能)
 - [x] 实现完整的key-value结构, 包括时间戳
 - [x] 读取一个配置文件
-- [ ] SkipList版 Memstore
+- [x] SkipList版 Memstore
 - [ ] 支持并发的 SkipList
 - [x] 有序SSTable结构
 - [ ] 集成Bloom Filter
diff --git a/skiplist.go b/skiplist.go
index ebadc93..106f052 100644
--- a/skiplist.go
+++ b/skiplist.go
@@ -25,13 +25,14 @@ type SkipListNode struct {
 // 一个完整的跳跃表结构
 type SkipList struct {
 	maxLevel int  // 最大的层级
+	len int  // 元素的个数
 	head, tail *SkipListNode  // 跳跃表的头和尾
 }
 
 // 这个maxLevel有一个默认值.
 // 这个值应该是可以配置的
 func NewSkipList() *SkipList {
-	sl := &SkipList{maxLevel: 3, head: &SkipListNode{key: "head"}, tail: &SkipListNode{key: "tail"}}
+	sl := &SkipList{maxLevel: 3, len: 0, head: &SkipListNode{key: "head"}, tail: &SkipListNode{key: "tail"}}
 	// 初始化 head和tail的指针
 	for i := 0; i <= sl.maxLevel; i++ {
 		sl.head.pointers = append(sl.head.pointers, sl.tail)
@@ -46,6 +47,7 @@ type pNode struct {
 
 // 插入一个KeyValue
 func (sl *SkipList) Put(kv KeyValue) {
+	sl.len++
 	key := kv.Key
 	p := sl.head
 	level := sl.maxLevel
@@ -145,6 +147,11 @@ func (sl *SkipList) FindGE(key string) KeyValue {
 	return KeyValue{}
 }
 
+// 元素的个数
+func (sl *SkipList) Len() int {
+	return sl.len
+}
+
 // 获取一个随机的高度值
 func (sl *SkipList) randHeight() int {
 	// 设置随机种子