这里我们用position:fixed；+ “hack技术” +“javascript”；结合来解决这一问题 
代码如下:
< html xmlns="http://www.w3.org/1999/xhtml">
< head>
< meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
< title>图胜前端工程师
< style type="text/css">
body,div{margin:0; padding:0;}
#a{width:200px;height:200px;background:blue;position:fixed;left:50%;top:50%;margin-left:-100px;margin-top:-100px;_position:absolute;}
< /style>
< script type="text/javascript">
var isIE=window.XMLHttpRequest?false:true;
var aIsIE={};
window.onload=function(){
if(isIE){
window.onscroll=doIE;
window.onresize=doIE; }
function doIE(){
aIsIE.top=document.documentElement.scrollTop;
aIsIE.left=document.documentElement.scrollLeft;
var width=document.documentElement.clientWidth;
var height=document.documentElement.clientHeight;
var oDiv=document.getElementById("a");
oDiv.style.top=aIsIE.top+(height-oDiv.offsetHeight)/2+'px';
oDiv.style.left=aIsIE.left+(width-oDiv.offsetWidth)/2+'px';< /script>
< /head>
< body style="width:100%;">
< div id="a">
< br/>
< /body>
< /html>
