diff --git a/structure/type.go b/structure/type.go
index 3411aad81703d..a79ef76350130 100644
--- a/structure/type.go
+++ b/structure/type.go
@@ -49,14 +49,14 @@ func (t *TxStructure) encodeStringDataKey(key []byte) kv.Key {
 }
 
 func (t *TxStructure) encodeHashMetaKey(key []byte) kv.Key {
-	ek := make([]byte, 0, len(t.prefix)+len(key)+24)
+	ek := make([]byte, 0, len(t.prefix)+codec.EncodedBytesLength(len(key))+8)
 	ek = append(ek, t.prefix...)
 	ek = codec.EncodeBytes(ek, key)
 	return codec.EncodeUint(ek, uint64(HashMeta))
 }
 
 func (t *TxStructure) encodeHashDataKey(key []byte, field []byte) kv.Key {
-	ek := make([]byte, 0, len(t.prefix)+len(key)+len(field)+30)
+	ek := make([]byte, 0, len(t.prefix)+codec.EncodedBytesLength(len(key))+8+codec.EncodedBytesLength(len(field)))
 	ek = append(ek, t.prefix...)
 	ek = codec.EncodeBytes(ek, key)
 	ek = codec.EncodeUint(ek, uint64(HashData))
diff --git a/util/codec/bytes.go b/util/codec/bytes.go
index 9ef8519dfb600..118c01ba0d1c8 100644
--- a/util/codec/bytes.go
+++ b/util/codec/bytes.go
@@ -67,6 +67,13 @@ func EncodeBytes(b []byte, data []byte) []byte {
 	return result
 }
 
+// EncodedBytesLength returns the length of data after encoded
+func EncodedBytesLength(dataLen int) int {
+	mod := dataLen % encGroupSize
+	padCount := encGroupSize - mod
+	return dataLen + padCount + 1 + dataLen/encGroupSize
+}
+
 func decodeBytes(b []byte, buf []byte, reverse bool) ([]byte, []byte, error) {
 	if buf == nil {
 		buf = make([]byte, 0, len(b))
diff --git a/util/codec/bytes_test.go b/util/codec/bytes_test.go
index 00b482e538141..68083040567d4 100644
--- a/util/codec/bytes_test.go
+++ b/util/codec/bytes_test.go
@@ -49,6 +49,9 @@ func (s *testBytesSuite) TestBytesCodec(c *C) {
 	}
 
 	for _, input := range inputs {
+
+		c.Assert(EncodedBytesLength(len(input.enc)), Equals, len(input.dec))
+
 		if input.desc {
 			b := EncodeBytesDesc(nil, input.enc)
 			c.Assert(b, BytesEquals, input.dec)