diff --git a/components/select/demo/optgroup.ts b/components/select/demo/optgroup.ts
index 31933a3b74f..d3d01b41e24 100644
--- a/components/select/demo/optgroup.ts
+++ b/components/select/demo/optgroup.ts
@@ -3,7 +3,7 @@ import { Component } from '@angular/core';
 @Component({
   selector: 'nz-demo-select-optgroup',
   template: `
-    <nz-select [(ngModel)]="selectedValue" nzAllowClear nzPlaceHolder="Choose">
+    <nz-select [(ngModel)]="selectedValue" nzAllowClear nzPlaceHolder="Choose" nzShowSearch>
       <nz-option-group nzLabel="Manager">
         <nz-option nzValue="jack" nzLabel="Jack"></nz-option>
         <nz-option nzValue="lucy" nzLabel="Lucy"></nz-option>
diff --git a/components/select/select.component.ts b/components/select/select.component.ts
index 64ad3afb9b2..f402c4d698d 100644
--- a/components/select/select.component.ts
+++ b/components/select/select.component.ts
@@ -304,8 +304,10 @@ export class NzSelectComponent implements ControlValueAccessor, OnInit, AfterVie
     /** insert group item **/
     listOfGroupLabel.forEach(label => {
       const index = listOfContainerItem.findIndex(item => label === item.groupLabel);
-      const groupItem = { groupLabel: label, type: 'group', key: label } as NzSelectItemInterface;
-      listOfContainerItem.splice(index, 0, groupItem);
+      if (index > -1) {
+        const groupItem = { groupLabel: label, type: 'group', key: label } as NzSelectItemInterface;
+        listOfContainerItem.splice(index, 0, groupItem);
+      }
     });
     this.listOfContainerItem = [...listOfContainerItem];
     this.updateCdkConnectedOverlayPositions();