diff --git a/leveldb/db.go b/leveldb/db.go
index 0fa0462..a7a3221 100644
--- a/leveldb/db.go
+++ b/leveldb/db.go
@@ -115,6 +115,13 @@ func (db *DB) Destroy() {
 	levigo.DestroyDatabase(db.cfg.Path, opts)
 }
 
+func (db *DB) Clear() {
+	it := db.Iterator(NewRange(nil, nil), 0)
+	for ; it.Valid(); it.Next() {
+		db.Delete(it.Key())
+	}
+}
+
 func (db *DB) Put(key, value []byte) error {
 	return db.db.Put(db.writeOpts, key, value)
 }
@@ -134,21 +141,14 @@ func (db *DB) NewWriteBatch() *WriteBatch {
 	return wb
 }
 
-//[begin, end]  close(inclusive) interval
-//if begin is nil, we will seek to first
-//if end is nil, we will seek to last
 //limit <= 0, no limit
-func (db *DB) Iterator(begin []byte, end []byte, limit int) *Iterator {
-	return newIterator(db, db.iteratorOpts, begin, end, limit, forward)
+func (db *DB) Iterator(r *Range, limit int) *Iterator {
+	return newIterator(db, db.iteratorOpts, r, limit, forward)
 }
 
-//[rbegin, rend] close(inclusive) interval
-//rbegin should bigger than rend
-//if rbegin is nil, we will seek to last
-//if end is nil, we will seek to first
 //limit <= 0, no limit
-func (db *DB) ReverseIterator(rbegin []byte, rend []byte, limit int) *Iterator {
-	return newIterator(db, db.iteratorOpts, rbegin, rend, limit, backward)
+func (db *DB) ReverseIterator(r *Range, limit int) *Iterator {
+	return newIterator(db, db.iteratorOpts, r, limit, backward)
 }
 
 func (db *DB) NewSnapshot() *Snapshot {
diff --git a/leveldb/iterator.go b/leveldb/iterator.go
index 7cbc213..588f09b 100644
--- a/leveldb/iterator.go
+++ b/leveldb/iterator.go
@@ -8,11 +8,39 @@ import (
 const forward uint8 = 0
 const backward uint8 = 1
 
+//min must less or equal than max
+//MinEx if true, range is left open interval (min, ...
+//MaxEx if true, range is right open interval ..., max)
+//Default range is close interval
+type Range struct {
+	Min []byte
+	Max []byte
+
+	MinEx bool
+	MaxEx bool
+}
+
+func NewRange(min []byte, max []byte) *Range {
+	return &Range{min, max, false, false}
+}
+
+func NewOpenRange(min []byte, max []byte) *Range {
+	return &Range{min, max, true, true}
+}
+
+func NewLOpenRange(min []byte, max []byte) *Range {
+	return &Range{min, max, true, false}
+}
+
+func NewROpenRange(min []byte, max []byte) *Range {
+	return &Range{min, max, true, true}
+}
+
 type Iterator struct {
 	it *levigo.Iterator
 
-	start []byte
-	stop  []byte
+	r *Range
+
 	limit int
 
 	step int
@@ -21,31 +49,42 @@ type Iterator struct {
 	direction uint8
 }
 
-func newIterator(db *DB, opts *levigo.ReadOptions, start []byte, stop []byte, limit int, direction uint8) *Iterator {
+func newIterator(db *DB, opts *levigo.ReadOptions, r *Range, limit int, direction uint8) *Iterator {
 	it := new(Iterator)
 	it.it = db.db.NewIterator(opts)
 
-	it.start = start
-	it.stop = stop
+	it.r = r
 	it.limit = limit
 	it.direction = direction
 	it.step = 0
 
-	if start == nil {
-		if direction == forward {
+	if direction == forward {
+		if r.Min == nil {
 			it.it.SeekToFirst()
 		} else {
-			it.it.SeekToLast()
+			it.it.Seek(r.Min)
+
+			if r.MinEx {
+				if it.Valid() && bytes.Equal(it.Key(), r.Min) {
+					it.it.Next()
+				}
+			}
 		}
 	} else {
-		it.it.Seek(start)
-
-		if it.Valid() && !bytes.Equal(it.Key(), start) {
-			//for forward, key is the next bigger than start
-			//for backward, key is the next bigger than start, so must go prev
-			if direction == backward {
+		if r.Max == nil {
+			it.it.SeekToLast()
+		} else {
+			it.it.Seek(r.Max)
+			if it.Valid() && !bytes.Equal(it.Key(), r.Max) {
+				//key must bigger than max, so we must go prev
 				it.it.Prev()
 			}
+
+			if r.MaxEx {
+				if it.Valid() && bytes.Equal(it.Key(), r.Max) {
+					it.it.Prev()
+				}
+			}
 		}
 	}
 
@@ -62,12 +101,22 @@ func (it *Iterator) Valid() bool {
 	}
 
 	if it.direction == forward {
-		if it.stop != nil && bytes.Compare(it.Key(), it.stop) > 0 {
-			return false
+		if it.r.Max != nil {
+			r := bytes.Compare(it.Key(), it.r.Max)
+			if !it.r.MaxEx {
+				return !(r > 0)
+			} else {
+				return !(r >= 0)
+			}
 		}
 	} else {
-		if it.stop != nil && bytes.Compare(it.Key(), it.stop) < 0 {
-			return false
+		if it.r.Min != nil {
+			r := bytes.Compare(it.Key(), it.r.Min)
+			if !it.r.MinEx {
+				return !(r < 0)
+			} else {
+				return !(r <= 0)
+			}
 		}
 	}
 
diff --git a/leveldb/leveldb_test.go b/leveldb/leveldb_test.go
index 6bee93c..62f53b9 100644
--- a/leveldb/leveldb_test.go
+++ b/leveldb/leveldb_test.go
@@ -107,210 +107,118 @@ func TestBatch(t *testing.T) {
 	db.Delete(key1)
 }
 
-func TestIterator(t *testing.T) {
-	db := getTestDB()
-	for it := db.Iterator(nil, nil, 0); it.Valid(); it.Next() {
-		db.Delete(it.Key())
-	}
-
-	for i := 0; i < 10; i++ {
-		key := []byte(fmt.Sprintf("key_%d", i))
-		value := []byte(fmt.Sprintf("value_%d", i))
-		db.Put(key, value)
-	}
-
-	step := 0
-	var it *Iterator
-	for it = db.Iterator(nil, nil, 0); it.Valid(); it.Next() {
-		key := it.Key()
-		value := it.Value()
-
-		if string(key) != fmt.Sprintf("key_%d", step) {
-			t.Fatal(string(key), step)
-		}
-
-		if string(value) != fmt.Sprintf("value_%d", step) {
-			t.Fatal(string(value), step)
-		}
-
-		step++
+func checkIterator(it *Iterator, cv ...int) error {
+	v := make([]string, 0, len(cv))
+	for ; it.Valid(); it.Next() {
+		k := it.Key()
+		v = append(v, string(k))
 	}
 
 	it.Close()
 
-	step = 2
-	for it = db.Iterator([]byte("key_2"), nil, 3); it.Valid(); it.Next() {
-		key := it.Key()
-		value := it.Value()
+	if len(v) != len(cv) {
+		return fmt.Errorf("len error %d != %d", len(v), len(cv))
+	}
 
-		if string(key) != fmt.Sprintf("key_%d", step) {
-			t.Fatal(string(key), step)
+	for k, i := range cv {
+		if fmt.Sprintf("key_%d", i) != v[k] {
+			return fmt.Errorf("%s, %d", v[k], i)
 		}
-
-		if string(value) != fmt.Sprintf("value_%d", step) {
-			t.Fatal(string(value), step)
-		}
-
-		step++
-	}
-	it.Close()
-
-	if step != 5 {
-		t.Fatal("invalid step", step)
 	}
 
-	step = 2
-	for it = db.Iterator([]byte("key_2"), []byte("key_5"), 0); it.Valid(); it.Next() {
-		key := it.Key()
-		value := it.Value()
+	return nil
+}
 
-		if string(key) != fmt.Sprintf("key_%d", step) {
-			t.Fatal(string(key), step)
-		}
-
-		if string(value) != fmt.Sprintf("value_%d", step) {
-			t.Fatal(string(value), step)
-		}
-
-		step++
-	}
-	it.Close()
-
-	if step != 6 {
-		t.Fatal("invalid step", step)
-	}
-
-	step = 2
-	for it = db.Iterator([]byte("key_5"), []byte("key_2"), 0); it.Valid(); it.Next() {
-		step++
-	}
-	it.Close()
-
-	if step != 2 {
-		t.Fatal("must 0")
-	}
-
-	step = 9
-	for it = db.ReverseIterator(nil, nil, 0); it.Valid(); it.Next() {
-		key := it.Key()
-		value := it.Value()
-
-		if string(key) != fmt.Sprintf("key_%d", step) {
-			t.Fatal(string(key), step)
-		}
-
-		if string(value) != fmt.Sprintf("value_%d", step) {
-			t.Fatal(string(value), step)
-		}
-
-		step--
-	}
-	it.Close()
-
-	step = 5
-	for it = db.ReverseIterator([]byte("key_5"), nil, 3); it.Valid(); it.Next() {
-		key := it.Key()
-		value := it.Value()
-
-		if string(key) != fmt.Sprintf("key_%d", step) {
-			t.Fatal(string(key), step)
-		}
-
-		if string(value) != fmt.Sprintf("value_%d", step) {
-			t.Fatal(string(value), step)
-		}
-
-		step--
-	}
-	it.Close()
-
-	if step != 2 {
-		t.Fatal("invalid step", step)
-	}
-
-	step = 5
-	for it = db.ReverseIterator([]byte("key_5"), []byte("key_2"), 0); it.Valid(); it.Next() {
-		key := it.Key()
-		value := it.Value()
-
-		if string(key) != fmt.Sprintf("key_%d", step) {
-			t.Fatal(string(key), step)
-		}
-
-		if string(value) != fmt.Sprintf("value_%d", step) {
-			t.Fatal(string(value), step)
-		}
-
-		step--
-	}
-	it.Close()
-
-	if step != 1 {
-		t.Fatal("invalid step", step)
-	}
-
-	step = 5
-	for it = db.ReverseIterator([]byte("key_2"), []byte("key_5"), 0); it.Valid(); it.Next() {
-		step--
-	}
-	it.Close()
-
-	if step != 5 {
-		t.Fatal("must 5")
+func testKeyRange(min int, max int) *Range {
+	return &Range{
+		[]byte(fmt.Sprintf("key_%d", min)),
+		[]byte(fmt.Sprintf("key_%d", max)),
+		false,
+		false,
 	}
 }
 
-func TestIterator_2(t *testing.T) {
+func testLKeyRange(min int, max int) *Range {
+	r := testKeyRange(min, max)
+	r.MinEx = true
+	return r
+}
+
+func testRKeyRange(min int, max int) *Range {
+	r := testKeyRange(min, max)
+	r.MaxEx = true
+	return r
+}
+
+func testOpenKeyRange(min int, max int) *Range {
+	r := testKeyRange(min, max)
+	r.MinEx = true
+	r.MaxEx = true
+	return r
+}
+
+func TestIterator(t *testing.T) {
 	db := getTestDB()
-	for it := db.Iterator(nil, nil, 0); it.Valid(); it.Next() {
-		db.Delete(it.Key())
+
+	db.Clear()
+
+	for i := 0; i < 10; i++ {
+		key := []byte(fmt.Sprintf("key_%d", i))
+		value := []byte("")
+		db.Put(key, value)
 	}
 
-	db.Put([]byte("key_1"), []byte("value_1"))
-	db.Put([]byte("key_7"), []byte("value_9"))
-	db.Put([]byte("key_9"), []byte("value_9"))
+	var it *Iterator
 
-	it := db.Iterator([]byte("key_0"), []byte("key_8"), 0)
-	if !it.Valid() {
-		t.Fatal("must valid")
+	it = db.Iterator(testKeyRange(1, 5), 0)
+	if err := checkIterator(it, 1, 2, 3, 4, 5); err != nil {
+		t.Fatal(err)
 	}
 
-	if string(it.Key()) != "key_1" {
-		t.Fatal(string(it.Key()))
+	it = db.Iterator(testKeyRange(1, 9), 5)
+	if err := checkIterator(it, 1, 2, 3, 4, 5); err != nil {
+		t.Fatal(err)
 	}
 
-	it.Close()
-
-	it = db.ReverseIterator([]byte("key_8"), []byte("key_0"), 0)
-	if !it.Valid() {
-		t.Fatal("must valid")
+	it = db.Iterator(testLKeyRange(1, 5), 0)
+	if err := checkIterator(it, 2, 3, 4, 5); err != nil {
+		t.Fatal(err)
 	}
 
-	if string(it.Key()) != "key_7" {
-		t.Fatal(string(it.Key()))
+	it = db.Iterator(testRKeyRange(1, 5), 0)
+	if err := checkIterator(it, 1, 2, 3, 4); err != nil {
+		t.Fatal(err)
 	}
 
-	it.Close()
-
-	for it = db.Iterator(nil, nil, 0); it.Valid(); it.Next() {
-		db.Delete(it.Key())
+	it = db.Iterator(testOpenKeyRange(1, 5), 0)
+	if err := checkIterator(it, 2, 3, 4); err != nil {
+		t.Fatal(err)
 	}
 
-	it.Close()
-
-	it = db.Iterator([]byte("key_0"), []byte("key_8"), 0)
-	if it.Valid() {
-		t.Fatal("must not valid")
+	it = db.ReverseIterator(testKeyRange(1, 5), 0)
+	if err := checkIterator(it, 5, 4, 3, 2, 1); err != nil {
+		t.Fatal(err)
 	}
 
-	it.Close()
-
-	it = db.ReverseIterator([]byte("key_8"), []byte("key_0"), 0)
-	if it.Valid() {
-		t.Fatal("must not valid")
+	it = db.ReverseIterator(testKeyRange(1, 9), 5)
+	if err := checkIterator(it, 9, 8, 7, 6, 5); err != nil {
+		t.Fatal(err)
 	}
 
-	it.Close()
+	it = db.ReverseIterator(testLKeyRange(1, 5), 0)
+	if err := checkIterator(it, 5, 4, 3, 2); err != nil {
+		t.Fatal(err)
+	}
+
+	it = db.ReverseIterator(testRKeyRange(1, 5), 0)
+	if err := checkIterator(it, 4, 3, 2, 1); err != nil {
+		t.Fatal(err)
+	}
+
+	it = db.ReverseIterator(testOpenKeyRange(1, 5), 0)
+	if err := checkIterator(it, 4, 3, 2); err != nil {
+		t.Fatal(err)
+	}
 }
 
 func TestSnapshot(t *testing.T) {
@@ -331,36 +239,6 @@ func TestSnapshot(t *testing.T) {
 	} else if string(v) != string(value) {
 		t.Fatal(string(v))
 	}
-
-	found := false
-	var it *Iterator
-	for it = s.Iterator(nil, nil, 0); it.Valid(); it.Next() {
-		if string(it.Key()) == string(key) {
-			found = true
-			break
-		}
-	}
-
-	it.Close()
-
-	if !found {
-		t.Fatal("must found")
-	}
-
-	found = false
-	for it = s.ReverseIterator(nil, nil, 0); it.Valid(); it.Next() {
-		if string(it.Key()) == string(key) {
-			found = true
-			break
-		}
-	}
-
-	it.Close()
-
-	if !found {
-		t.Fatal("must found")
-	}
-
 }
 
 func TestDestroy(t *testing.T) {
diff --git a/leveldb/snapshot.go b/leveldb/snapshot.go
index ab7b37a..72eb40f 100644
--- a/leveldb/snapshot.go
+++ b/leveldb/snapshot.go
@@ -38,12 +38,12 @@ func (s *Snapshot) Get(key []byte) ([]byte, error) {
 }
 
 //same as db iterator and reverse iterator
-func (s *Snapshot) Iterator(begin []byte, end []byte, limit int) *Iterator {
-	return newIterator(s.db, s.iteratorOpts, begin, end, limit, forward)
+func (s *Snapshot) Iterator(r *Range, limit int) *Iterator {
+	return newIterator(s.db, s.iteratorOpts, r, limit, forward)
 }
 
-func (s *Snapshot) ReverseIterator(rbegin []byte, rend []byte, limit int) *Iterator {
-	return newIterator(s.db, s.iteratorOpts, rbegin, rend, limit, backward)
+func (s *Snapshot) ReverseIterator(r *Range, limit int) *Iterator {
+	return newIterator(s.db, s.iteratorOpts, r, limit, backward)
 }
 
 func (s *Snapshot) GetInt(key []byte) (int64, error) {