<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>顶部固定菜单</title>
<style type="text/css">
*{ margin:0; padding:0;}
.nav-wrapper-fixed{ position:fixed; top:0; width:100%;}
.nav-wrapper-fixed .nav{width:960px; margin:0 auto;}
.nav-wrapper-fixed .nav li{ float:left; width:100px; margin-right:5px; background:#CCC; text-align:center; height:24px; line-height:24px; list-style:none;}
.nav-wrapper{ margin-top:100px; width:100%;}
.nav-wrapper .nav{width:960px; margin:0 auto;}
.nav-wrapper .nav li{ float:left; width:100px; margin-right:5px; background:#CCC; text-align:center; height:24px; line-height:24px; list-style:none;}
</style>
<script type="text/javascript">
window.onload=function(){
    var nav=document.getElementById('nav');
    var navFixed=document.getElementById('navFixed');
    window.onscroll=function(){
        var scrollTop=document.documentElement.scrollTop||document.body.scrollTop;
        document.title=scrollTop
        if(scrollTop>nav.offsetTop){
            navFixed.style.display='block';
        }else if(scrollTop<nav.offsetTop){
            navFixed.style.display='none';
        }
    }
};
</script>
</head>
<body style="height:2000px;">
<div class="nav-wrapper">
    <div class="nav" id="nav">
        <ul>
            <li>菜单一</li>
            <li>菜单二</li>
            <li>菜单三</li>
            <li>菜单四</li>
            <li>菜单五</li>
        </ul>
    </div>
</div>
<div class="nav-wrapper-fixed" id="navFixed" style="display:none;">
    <div class="nav" id="nav">
        <ul>
            <li>菜单一</li>
            <li>菜单二</li>
            <li>菜单三</li>
            <li>菜单四</li>
            <li>菜单五</li>
        </ul>
    </div>
</div>
</body>
</html>