diff --git a/database/set.go b/database/set.go
index 41282fb..b283a0d 100644
--- a/database/set.go
+++ b/database/set.go
@@ -179,38 +179,10 @@ func execSMembers(db *DB, args [][]byte) redis.Reply {
 	return protocol.MakeMultiBulkReply(arr)
 }
 
-// execSInter intersect multiple sets
-func execSInter(db *DB, args [][]byte) redis.Reply {
-	keys := make([]string, len(args))
-	for i, arg := range args {
-		keys[i] = string(arg)
-	}
-
-	var result *HashSet.Set
-	for _, key := range keys {
-		set, errReply := db.getAsSet(key)
-		if errReply != nil {
-			return errReply
-		}
-		if set == nil {
-			return &protocol.EmptyMultiBulkReply{}
-		}
-
-		if result == nil {
-			// init
-			result = HashSet.Make(set.ToSlice()...)
-		} else {
-			result = result.Intersect(set)
-			if result.Len() == 0 {
-				// early termination
-				return &protocol.EmptyMultiBulkReply{}
-			}
-		}
-	}
-
-	arr := make([][]byte, result.Len())
+func set2reply(set *HashSet.Set) redis.Reply {
+	arr := make([][]byte, set.Len())
 	i := 0
-	result.ForEach(func(member string) bool {
+	set.ForEach(func(member string) bool {
 		arr[i] = []byte(member)
 		i++
 		return true
@@ -218,221 +190,125 @@ func execSInter(db *DB, args [][]byte) redis.Reply {
 	return protocol.MakeMultiBulkReply(arr)
 }
 
+// execSInter intersect multiple sets
+func execSInter(db *DB, args [][]byte) redis.Reply {
+	sets := make([]*HashSet.Set, 0, len(args))
+	for _, arg := range args {
+		key := string(arg)
+		set, errReply := db.getAsSet(key)
+		if errReply != nil {
+			return errReply
+		}
+		if set.Len() == 0 {
+			return &protocol.EmptyMultiBulkReply{}
+		}
+		sets = append(sets, set)
+	}
+	result := HashSet.Intersect(sets...)
+	return set2reply(result)
+}
+
 // execSInterStore intersects multiple sets and store the result in a key
 func execSInterStore(db *DB, args [][]byte) redis.Reply {
 	dest := string(args[0])
-	keys := make([]string, len(args)-1)
-	keyArgs := args[1:]
-	for i, arg := range keyArgs {
-		keys[i] = string(arg)
-	}
-
-	var result *HashSet.Set
-	for _, key := range keys {
+	sets := make([]*HashSet.Set, 0, len(args)-1)
+	for i := 1; i < len(args); i++ {
+		key := string(args[i])
 		set, errReply := db.getAsSet(key)
 		if errReply != nil {
 			return errReply
 		}
-		if set == nil {
-			db.Remove(dest) // clean ttl and old value
+		if set.Len() == 0 {
 			return protocol.MakeIntReply(0)
 		}
-
-		if result == nil {
-			// init
-			result = HashSet.Make(set.ToSlice()...)
-		} else {
-			result = result.Intersect(set)
-			if result.Len() == 0 {
-				// early termination
-				db.Remove(dest) // clean ttl and old value
-				return protocol.MakeIntReply(0)
-			}
-		}
+		sets = append(sets, set)
 	}
+	result := HashSet.Intersect(sets...)
 
-	set := HashSet.Make(result.ToSlice()...)
 	db.PutEntity(dest, &database.DataEntity{
-		Data: set,
+		Data: result,
 	})
 	db.addAof(utils.ToCmdLine3("sinterstore", args...))
-	return protocol.MakeIntReply(int64(set.Len()))
+	return protocol.MakeIntReply(int64(result.Len()))
 }
 
 // execSUnion adds multiple sets
 func execSUnion(db *DB, args [][]byte) redis.Reply {
-	keys := make([]string, len(args))
-	for i, arg := range args {
-		keys[i] = string(arg)
-	}
-
-	var result *HashSet.Set
-	for _, key := range keys {
+	sets := make([]*HashSet.Set, 0, len(args))
+	for _, arg := range args {
+		key := string(arg)
 		set, errReply := db.getAsSet(key)
 		if errReply != nil {
 			return errReply
 		}
-		if set == nil {
-			continue
-		}
-
-		if result == nil {
-			// init
-			result = HashSet.Make(set.ToSlice()...)
-		} else {
-			result = result.Union(set)
-		}
+		sets = append(sets, set)
 	}
-
-	if result == nil {
-		// all keys are empty set
-		return &protocol.EmptyMultiBulkReply{}
-	}
-	arr := make([][]byte, result.Len())
-	i := 0
-	result.ForEach(func(member string) bool {
-		arr[i] = []byte(member)
-		i++
-		return true
-	})
-	return protocol.MakeMultiBulkReply(arr)
+	result := HashSet.Union(sets...)
+	return set2reply(result)
 }
 
 // execSUnionStore adds multiple sets and store the result in a key
 func execSUnionStore(db *DB, args [][]byte) redis.Reply {
 	dest := string(args[0])
-	keys := make([]string, len(args)-1)
-	keyArgs := args[1:]
-	for i, arg := range keyArgs {
-		keys[i] = string(arg)
-	}
-
-	var result *HashSet.Set
-	for _, key := range keys {
+	sets := make([]*HashSet.Set, 0, len(args)-1)
+	for i := 1; i < len(args); i++ {
+		key := string(args[i])
 		set, errReply := db.getAsSet(key)
 		if errReply != nil {
 			return errReply
 		}
-		if set == nil {
-			continue
-		}
-		if result == nil {
-			// init
-			result = HashSet.Make(set.ToSlice()...)
-		} else {
-			result = result.Union(set)
-		}
+		sets = append(sets, set)
 	}
-
+	result := HashSet.Union(sets...)
 	db.Remove(dest) // clean ttl
-	if result == nil {
-		// all keys are empty set
-		return &protocol.EmptyMultiBulkReply{}
+	if result.Len() == 0 {
+		return protocol.MakeIntReply(0)
 	}
 
-	set := HashSet.Make(result.ToSlice()...)
 	db.PutEntity(dest, &database.DataEntity{
-		Data: set,
+		Data: result,
 	})
-
 	db.addAof(utils.ToCmdLine3("sunionstore", args...))
-	return protocol.MakeIntReply(int64(set.Len()))
+	return protocol.MakeIntReply(int64(result.Len()))
 }
 
 // execSDiff subtracts multiple sets
 func execSDiff(db *DB, args [][]byte) redis.Reply {
-	keys := make([]string, len(args))
-	for i, arg := range args {
-		keys[i] = string(arg)
-	}
-
-	var result *HashSet.Set
-	for i, key := range keys {
+	sets := make([]*HashSet.Set, 0, len(args))
+	for _, arg := range args {
+		key := string(arg)
 		set, errReply := db.getAsSet(key)
 		if errReply != nil {
 			return errReply
 		}
-		if set == nil {
-			if i == 0 {
-				// early termination
-				return &protocol.EmptyMultiBulkReply{}
-			}
-			continue
-		}
-		if result == nil {
-			// init
-			result = HashSet.Make(set.ToSlice()...)
-		} else {
-			result = result.Diff(set)
-			if result.Len() == 0 {
-				// early termination
-				return &protocol.EmptyMultiBulkReply{}
-			}
-		}
+		sets = append(sets, set)
 	}
-
-	if result == nil {
-		// all keys are nil
-		return &protocol.EmptyMultiBulkReply{}
-	}
-	arr := make([][]byte, result.Len())
-	i := 0
-	result.ForEach(func(member string) bool {
-		arr[i] = []byte(member)
-		i++
-		return true
-	})
-	return protocol.MakeMultiBulkReply(arr)
+	result := HashSet.Diff(sets...)
+	return set2reply(result)
 }
 
 // execSDiffStore subtracts multiple sets and store the result in a key
 func execSDiffStore(db *DB, args [][]byte) redis.Reply {
 	dest := string(args[0])
-	keys := make([]string, len(args)-1)
-	keyArgs := args[1:]
-	for i, arg := range keyArgs {
-		keys[i] = string(arg)
-	}
-
-	var result *HashSet.Set
-	for i, key := range keys {
+	sets := make([]*HashSet.Set, 0, len(args)-1)
+	for i := 1; i < len(args); i++ {
+		key := string(args[i])
 		set, errReply := db.getAsSet(key)
 		if errReply != nil {
 			return errReply
 		}
-		if set == nil {
-			if i == 0 {
-				// early termination
-				db.Remove(dest)
-				return protocol.MakeIntReply(0)
-			}
-			continue
-		}
-		if result == nil {
-			// init
-			result = HashSet.Make(set.ToSlice()...)
-		} else {
-			result = result.Diff(set)
-			if result.Len() == 0 {
-				// early termination
-				db.Remove(dest)
-				return protocol.MakeIntReply(0)
-			}
-		}
+		sets = append(sets, set)
 	}
-
-	if result == nil {
-		// all keys are nil
-		db.Remove(dest)
-		return &protocol.EmptyMultiBulkReply{}
+	result := HashSet.Diff(sets...)
+	db.Remove(dest) // clean ttl
+	if result.Len() == 0 {
+		return protocol.MakeIntReply(0)
 	}
-	set := HashSet.Make(result.ToSlice()...)
 	db.PutEntity(dest, &database.DataEntity{
-		Data: set,
+		Data: result,
 	})
-
 	db.addAof(utils.ToCmdLine3("sdiffstore", args...))
-	return protocol.MakeIntReply(int64(set.Len()))
+	return protocol.MakeIntReply(int64(result.Len()))
 }
 
 // execSRandMember gets random members from set
diff --git a/database/set_test.go b/database/set_test.go
index a4a3561..638e0ac 100644
--- a/database/set_test.go
+++ b/database/set_test.go
@@ -106,7 +106,7 @@ func TestSInter(t *testing.T) {
 	keys := make([]string, 0)
 	start := 0
 	for i := 0; i < 4; i++ {
-		key := utils.RandString(10)
+		key := utils.RandString(10) + strconv.Itoa(i)
 		keys = append(keys, key)
 		for j := start; j < size+start; j++ {
 			member := strconv.Itoa(j)
diff --git a/datastruct/set/set.go b/datastruct/set/set.go
index 50f29f1..2b1648b 100644
--- a/datastruct/set/set.go
+++ b/datastruct/set/set.go
@@ -1,6 +1,8 @@
 package set
 
-import "github.com/hdt3213/godis/datastruct/dict"
+import (
+	"github.com/hdt3213/godis/datastruct/dict"
+)
 
 // Set is a set of elements based on hash table
 type Set struct {
@@ -30,12 +32,18 @@ func (set *Set) Remove(val string) int {
 
 // Has returns true if the val exists in the set
 func (set *Set) Has(val string) bool {
+	if set == nil || set.dict == nil {
+		return false
+	}
 	_, exists := set.dict.Get(val)
 	return exists
 }
 
 // Len returns number of members in the set
 func (set *Set) Len() int {
+	if set == nil || set.dict == nil {
+		return 0
+	}
 	return set.dict.Len()
 }
 
@@ -58,62 +66,81 @@ func (set *Set) ToSlice() []string {
 
 // ForEach visits each member in the set
 func (set *Set) ForEach(consumer func(member string) bool) {
+	if set == nil || set.dict == nil {
+		return
+	}
 	set.dict.ForEach(func(key string, val interface{}) bool {
 		return consumer(key)
 	})
 }
 
-// Intersect intersects two sets
-func (set *Set) Intersect(another *Set) *Set {
-	if set == nil {
-		panic("set is nil")
-	}
-
+// ShallowCopy copies all members to another set
+func (set *Set) ShallowCopy() *Set {
 	result := Make()
-	another.ForEach(func(member string) bool {
-		if set.Has(member) {
-			result.Add(member)
-		}
+	set.ForEach(func(member string) bool {
+		result.Add(member)
 		return true
 	})
 	return result
 }
 
+// Intersect intersects two sets
+func Intersect(sets ...*Set) *Set {
+	result := Make()
+	if len(sets) == 0 {
+		return result
+	}
+
+	countMap := make(map[string]int)
+	for _, set := range sets {
+		set.ForEach(func(member string) bool {
+			countMap[member]++
+			return true
+		})
+	}
+	for k, v := range countMap {
+		if v == len(sets) {
+			result.Add(k)
+		}
+	}
+	return result
+}
+
 // Union adds two sets
-func (set *Set) Union(another *Set) *Set {
-	if set == nil {
-		panic("set is nil")
-	}
+func Union(sets ...*Set) *Set {
 	result := Make()
-	another.ForEach(func(member string) bool {
-		result.Add(member)
-		return true
-	})
-	set.ForEach(func(member string) bool {
-		result.Add(member)
-		return true
-	})
+	for _, set := range sets {
+		set.ForEach(func(member string) bool {
+			result.Add(member)
+			return true
+		})
+	}
 	return result
 }
 
 // Diff subtracts two sets
-func (set *Set) Diff(another *Set) *Set {
-	if set == nil {
-		panic("set is nil")
+func Diff(sets ...*Set) *Set {
+	if len(sets) == 0 {
+		return Make()
 	}
-
-	result := Make()
-	set.ForEach(func(member string) bool {
-		if !another.Has(member) {
-			result.Add(member)
+	result := sets[0].ShallowCopy()
+	for i := 1; i < len(sets); i++ {
+		sets[i].ForEach(func(member string) bool {
+			result.Remove(member)
+			return true
+		})
+		if result.Len() == 0 {
+			break
 		}
-		return true
-	})
+	}
 	return result
 }
 
 // RandomMembers randomly returns keys of the given number, may contain duplicated key
 func (set *Set) RandomMembers(limit int) []string {
+	if set == nil || set.dict == nil {
+		return nil
+	}
 	return set.dict.RandomKeys(limit)
 }