<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style type="text/css">
*{margin: 0; padding: 0;}
.box{ 960px; height: 1800px; background: #F29292; margin: 0 auto; }
.gotop{ 60px; height: 60px; background: red; position: fixed; left: 50%; bottom: 50px; margin-left: 480px; display: none; }
</style>
<script src="http://apps.bdimg.com/libs/jquery/1.9.1/jquery.min.js" type="text/javascript"></script>
<script type="text/javascript">
$(function() {
//scroll 事件适用于所有可滚动的元素和 window 对象（浏览器窗口）。
$(window).scroll(function() {
var scroHei = $(window).scrollTop();//滚动的高度
if (scroHei > 400) {
$('.J_goTop').fadeIn();
} else {
$('.J_goTop').fadeOut();
}
})
/*点击返回顶部*/
$('.J_goTop').click(function() {
$('body,html').animate({
scrollTop: 0
}, 600);
})
})
</script>
</head>
<body>
<div class="box"></div>
<div class="gotop J_goTop">返回顶部</div>
</body>
</html>
如图：
