diff --git a/pkg/schedule/operator/operator_controller.go b/pkg/schedule/operator/operator_controller.go
index f05c232904f..b9294ad970d 100644
--- a/pkg/schedule/operator/operator_controller.go
+++ b/pkg/schedule/operator/operator_controller.go
@@ -324,14 +324,16 @@ func (oc *Controller) AddWaitingOperator(ops ...*Operator) int {
 			}
 			continue
 		}
-		oc.wop.PutOperator(op)
+
 		if isMerge {
 			// count two merge operators as one, so wopStatus.ops[desc] should
 			// not be updated here
 			// TODO: call checkAddOperator ...
+			oc.wop.PutMergeOperators([]*Operator{op, ops[i+1]})
 			i++
 			added++
-			oc.wop.PutOperator(ops[i])
+		} else {
+			oc.wop.PutOperator(op)
 		}
 		operatorCounter.WithLabelValues(desc, "put").Inc()
 		oc.wopStatus.incCount(desc)
diff --git a/pkg/schedule/operator/waiting_operator.go b/pkg/schedule/operator/waiting_operator.go
index b3b1b885663..f75dcf25cd8 100644
--- a/pkg/schedule/operator/waiting_operator.go
+++ b/pkg/schedule/operator/waiting_operator.go
@@ -26,6 +26,7 @@ var priorityWeight = []float64{1.0, 4.0, 9.0, 16.0}
 // WaitingOperator is an interface of waiting operators.
 type WaitingOperator interface {
 	PutOperator(op *Operator)
+	PutMergeOperators(op []*Operator)
 	GetOperator() []*Operator
 	ListOperator() []*Operator
 }
@@ -66,6 +67,21 @@ func (b *randBuckets) PutOperator(op *Operator) {
 	bucket.ops = append(bucket.ops, op)
 }
 
+// PutMergeOperators puts two operators into the random buckets.
+func (b *randBuckets) PutMergeOperators(ops []*Operator) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if len(ops) != 2 && (ops[0].Kind()&OpMerge == 0 || ops[1].Kind()&OpMerge == 0) {
+		return
+	}
+	priority := ops[0].GetPriorityLevel()
+	bucket := b.buckets[priority]
+	if len(bucket.ops) == 0 {
+		b.totalWeight += bucket.weight
+	}
+	bucket.ops = append(bucket.ops, ops...)
+}
+
 // ListOperator lists all operator in the random buckets.
 func (b *randBuckets) ListOperator() []*Operator {
 	b.mu.Lock()