在网上找到不少用js写的。这个用css写的，在别人网站上找到，把内容精简了
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="test_Default" %>
<!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 runat="server">
<title>无标题页</title>
<style type="text/css">
#sticky_footer
{
width: 100%;
background-color: #eee;
opacity:.8;
filter:alpha(opacity=80);
-moz-opacity: 0.8;
position: fixed;
_position:absolute;
overflow: hidden;
height:38px;
bottom: 0;
z-index: 99999;
line-height:38px;
float:left;
_top:expression(eval(document.documentElement.scrollTop+document.documentElement.clientHeight-this.offsetHeight-(parseInt(this.currentStyle.marginTop,10)||0)-(parseInt(this.currentStyle.marginBottom,10)||0)));
}
#wrapperfooter{width:960px;margin:0 auto;border-top:0px #e5e5e5 solid;padding:0;}
</style>
</head>
<body>
<form id="form1" runat="server">
<div style="height:900px; background-color:Blue">
</div>
<div style="height:90px;">
</div>
<div id="sticky_footer">
<div id="wrapperfooter">
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
</div>
</div>
</form>
</body>
</html>
<!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 runat="server">
<title>无标题页</title>
<style type="text/css">
#sticky_footer
{
width: 100%;
background-color: #eee;
opacity:.8;
filter:alpha(opacity=80);
-moz-opacity: 0.8;
position: fixed;
_position:absolute;
overflow: hidden;
height:38px;
bottom: 0;
z-index: 99999;
line-height:38px;
float:left;
_top:expression(eval(document.documentElement.scrollTop+document.documentElement.clientHeight-this.offsetHeight-(parseInt(this.currentStyle.marginTop,10)||0)-(parseInt(this.currentStyle.marginBottom,10)||0)));
}
#wrapperfooter{width:960px;margin:0 auto;border-top:0px #e5e5e5 solid;padding:0;}
</style>
</head>
<body>
<form id="form1" runat="server">
<div style="height:900px; background-color:Blue">
</div>
<div style="height:90px;">
</div>
<div id="sticky_footer">
<div id="wrapperfooter">
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
</div>
</div>
</form>
</body>
</html>