1.html

<div id='returnTool'>返回顶部</div>

2.css （将returnTool层至于页面底部固定不动）

<style type="text/css">
#returnTool { 
	position:absolute; 
	margin-bottom:0px;
	width:95%; 
	height:100px; 
	text-align:right;
	z-index:2; 
	overflow:hidden; 
	cursor: pointer;
} 
</style>

3.js

<script type="text/javascript">
$("#returnTool").click(function () {
	$("html,body").animate({scrollTop:"0px"},50);//50毫秒完成回到顶部动画
})
</script>