diff --git a/components/select/demo/automatic-tokenization.ts b/components/select/demo/automatic-tokenization.ts
index d0b8951f73d..77654faf59f 100644
--- a/components/select/demo/automatic-tokenization.ts
+++ b/components/select/demo/automatic-tokenization.ts
@@ -3,14 +3,20 @@ import { Component, OnInit } from '@angular/core';
 @Component({
   selector: 'nz-demo-select-automatic-tokenization',
   template: `
-    <nz-select nzMode="tags" [nzTokenSeparators]="[',']" style="width: 100%;" [(ngModel)]="listOfTagOptions">
+    <nz-select
+      nzMode="tags"
+      [nzTokenSeparators]="[',']"
+      style="width: 100%;"
+      [(ngModel)]="listOfTagOptions"
+      nzPlaceHolder="automatic tokenization"
+    >
       <nz-option *ngFor="let option of listOfOption" [nzLabel]="option.label" [nzValue]="option.value"> </nz-option>
     </nz-select>
   `
 })
 export class NzDemoSelectAutomaticTokenizationComponent implements OnInit {
   listOfOption: Array<{ label: string; value: string }> = [];
-  listOfTagOptions = null;
+  listOfTagOptions = [];
 
   ngOnInit(): void {
     const children: Array<{ label: string; value: string }> = [];
diff --git a/components/select/demo/select-users.ts b/components/select/demo/select-users.ts
index 9ad830a11b6..3bf53ab38f2 100644
--- a/components/select/demo/select-users.ts
+++ b/components/select/demo/select-users.ts
@@ -36,7 +36,7 @@ export class NzDemoSelectSelectUsersComponent implements OnInit {
   randomUserUrl = 'https://api.randomuser.me/?results=5';
   searchChange$ = new BehaviorSubject('');
   optionList: string[] = [];
-  selectedUser = '';
+  selectedUser: string;
   isLoading = false;
 
   onSearch(value: string): void {
diff --git a/components/select/nz-option-container.component.ts b/components/select/nz-option-container.component.ts
index ed75b41b080..1da854c1539 100644
--- a/components/select/nz-option-container.component.ts
+++ b/components/select/nz-option-container.component.ts
@@ -31,6 +31,7 @@ import { NzSelectService } from './nz-select.service';
 })
 export class NzOptionContainerComponent implements OnDestroy, OnInit {
   private destroy$ = new Subject();
+  private lastScrollTop = 0;
   @ViewChildren(NzOptionLiComponent) listOfNzOptionLiComponent: QueryList<NzOptionLiComponent>;
   @ViewChild('dropdownUl') dropdownUl: ElementRef;
   @Input() nzNotFoundContent: string;
@@ -78,7 +79,8 @@ export class NzOptionContainerComponent implements OnDestroy, OnInit {
         .subscribe(e => {
           e.preventDefault();
           e.stopPropagation();
-          if (ul && ul.scrollHeight < ul.clientHeight + ul.scrollTop + 10) {
+          if (ul && ul.scrollTop > this.lastScrollTop && ul.scrollHeight < ul.clientHeight + ul.scrollTop + 10) {
+            this.lastScrollTop = ul.scrollTop;
             this.ngZone.run(() => {
               this.nzScrollToBottom.emit();
             });