设置示例：
<div id="a1" style="position:absolute;left:100px;top:100px;width:100px;height:100px; background-color:#ddeeff;z-index:1"></div> <div id="a2" style="position:absolute;left:150px;top:130px;width:100px;height:100px; background-color:#eeffdd;z-index:2"></div> <div id="a3" style="position:absolute;left:200px;top:160px;width:100px;height:100px; background-color:#ffddee;z-index:3"></div>
DEMO：
<html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=gb2312" /> <title></title> <script type="text/javascript"> function $(obj){ return document.getElementById(obj); } function change(n){ for (var i=1;i<4;i++){ if(n==i){ $("a"+i).style.zIndex="100"; }else{ $("a"+i).style.zIndex="0"; } } } </script> </head> <body> <div id="a1" style="position:absolute;left:100px;top:100px;width:100px;height:100px; background-color:#ddeeff;z-index:1" onclick="change('1')" ></div> <div id="a2" style="position:absolute;left:150px;top:130px;width:100px;height:100px; background-color:#eeffdd;z-index:2" onclick="change('2')"></div> <div id="a3" style="position:absolute;left:200px;top:160px;width:100px;height:100px; background-color:#ffddee;z-index:3" onclick="change('3')"></div> </body> </html>
原文链接：http://hi.baidu.com/j_z_/blog/item/458dd81b98821dd0ac6e756a.html