<div style=" position: fixed; width: 100%; height: 100%; left: 0px; top: 0px; background-color: Black; z-index: 9999; filter: alpha(opacity=70); Opacity:0.7;"></div>
z-index 必须大于遮罩元素
demo
<!doctype html> <html> <head> <meta charset="utf-8"> <title>无标题文档</title> <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1" /> <meta name="apple-mobile-web-app-capable" content="yes" /> <script type="text/javascript" src="jquery-1.7.2.min.js"></script> <style type="text/css"> ul, ul ul { list-style-type:none; margin: 0; padding: 0; width: 15em; } ul a { display: block; text-decoration: none; } ul li { margin-top: 1px; } ul li a { background: #333; color: #fff; padding: 0.5em; } ul li a:hover { background: #000; } ul li ul li a { background: #ccc; color: #000; padding-left: 20px; } ul li ul li a:hover,ul li ul .current a { background: #aaa; border-left: 5px #000 solid; padding-left: 15px; } </style> </head> <body> <div id="bb" style="background-color: red;display:none;z-index: 99999; max-height:79.3%; position: fixed; filter: alpha(opacity=70); Opacity:0.7; top: 10px; left:5px;"> <ul> <li> <a href="">老大</a> <ul> <li> <a href="javascript:alert('you can do you want');">老大大</a> <li> <li> <a href="javascript:alert('you can do you want');">老大二</a> <li> <li> <a href="javascript:alert('you can do you want');">老大三</a> <li> <li> <a href="javascript:alert('you can do you want');">老大四</a> <li> </ul> <li> <li> <a href="javascript:alert('you can do you want');">老二</a> <li> <li> <a href="javascript:alert('you can do you want');">老三</a> <li> <li> <a href="">老四</a> <ul > <li><a href="javascript:alert('you can do you want');">老一</a><li> </ul> <li> </ul> </div> <br> <br> <br> <br> <br> <br> <br> <br><br><br> <br> <br> <button id="aa">哈哈</button> <div id="zz" style="display:none;position: fixed; width: 100%; height: 100%; left: 0px; top: 0px; background-color: Black; z-index: 1999; filter: alpha(opacity=70); Opacity:0.7;"></div> </body> <script type="text/javascript"> $(function(){ $("#aa").click(function(){ $("#zz").show(); $("#bb").show(); $("#bb").animate({left:'100px'}); $("#bb").animate({left:'0px'}); }); $("#zz").click(function(){ $("#bb").animate({left:'-240px'}); $("#zz").hide(); }); $('#bb ul li ul').hide(); $("#bb ul li a").click(function(){ var a= $(this); var nextobj=a.next(); if(nextobj.is("ul")){ $('#bb ul li ul:visible').slideUp('normal'); if(!nextobj.is(':visible')){ nextobj.slideDown('normal'); } return false; } }); }); </script> </html>