diff --git a/pkg/webhook/server/generic/operationjob/operationjob_validating_handler.go b/pkg/webhook/server/generic/operationjob/operationjob_validating_handler.go
index 81676ac3..8c7e0d44 100644
--- a/pkg/webhook/server/generic/operationjob/operationjob_validating_handler.go
+++ b/pkg/webhook/server/generic/operationjob/operationjob_validating_handler.go
@@ -26,6 +26,7 @@ import (
 	"k8s.io/apimachinery/pkg/api/equality"
 	"k8s.io/apimachinery/pkg/util/sets"
 	"k8s.io/apimachinery/pkg/util/validation/field"
+	"k8s.io/utils/ptr"
 	"sigs.k8s.io/controller-runtime/pkg/runtime/inject"
 	"sigs.k8s.io/controller-runtime/pkg/webhook/admission"
 
@@ -127,29 +128,14 @@ func (h *ValidatingHandler) validateOpsTarget(instance, old *appsv1alpha1.Operat
 
 func (h *ValidatingHandler) validatePartition(instance, old *appsv1alpha1.OperationJob, fldPath *field.Path) field.ErrorList {
 	var allErrors field.ErrorList
-	var currPartition, oldPartition int32
-	var currTotalReplicas, oldTotalReplicas int32
-
-	currTotalReplicas = int32(len(instance.Spec.Targets))
-	if instance.Spec.Partition == nil {
-		currPartition = currTotalReplicas
-	} else {
-		currPartition = minInt32(*instance.Spec.Partition, currTotalReplicas)
-	}
-
-	oldTotalReplicas = int32(len(old.Spec.Targets))
-	if old.Spec.Partition == nil {
-		oldPartition = oldTotalReplicas
-	} else {
-		oldPartition = minInt32(*old.Spec.Partition, oldTotalReplicas)
-	}
+	oldPartition := ptr.Deref(old.Spec.Partition, 0)
+	curPartition := ptr.Deref(instance.Spec.Partition, 0)
 
-	if currPartition < 0 {
-		allErrors = append(allErrors, field.Invalid(fldPath.Child("partition"), currPartition, "should not be negative"))
-	} else if currPartition < oldPartition {
-		allErrors = append(allErrors, field.Invalid(fldPath.Child("partition"), currPartition, fmt.Sprintf("should not be decreased (from %d to %d)", oldPartition, currPartition)))
+	if curPartition < 0 {
+		allErrors = append(allErrors, field.Invalid(fldPath, curPartition, "should not be negative"))
+	} else if oldPartition > curPartition {
+		allErrors = append(allErrors, field.Invalid(fldPath, curPartition, fmt.Sprintf("should not be decreased. (from %d to %d)", oldPartition, curPartition)))
 	}
-
 	return allErrors
 }
 
@@ -165,10 +151,3 @@ func (h *ValidatingHandler) validateTTLAndActiveDeadline(instance *appsv1alpha1.
 	}
 	return allErrors
 }
-
-func minInt32(a, b int32) int32 {
-	if a < b {
-		return a
-	}
-	return b
-}