<!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>无标题文档</title>
<script>
function GetDateDiff() {
var date1 = new Date(); //开始时间
var date2 = new Date("2012-12-31".replace(/-/g, "/")); //结束时间
var date3 = date2.getTime() - date1.getTime(); //时间差的毫秒数
//计算出相差天数
var days = Math.floor(date3 / (24 * 3600 * 1000));
//计算出小时数
var leave1 = date3 % (24 * 3600 * 1000);
//计算天数后剩余的毫秒数
var hours = Math.floor(leave1 / (3600 * 1000));
//计算相差分钟数
var leave2 = leave1 % (3600 * 1000); //计算小时数后剩余的毫秒数
var minutes = Math.floor(leave2 / (60 * 1000));
//计算相差秒数
var leave3 = leave2 % (60 * 1000);
//计算分钟数后剩余的毫秒数
var seconds = Math.round(leave3 / 1000);
document.getElementById("time").value = days + "天 " + hours + "小时 " + minutes + " 分钟" + seconds + " 秒";
}
setInterval("GetDateDiff()", 1000);
</script>
</head>
<body>
<input name="time" id="time" type="text" />
</body>
</html>
参考：http://www.cnblogs.com/bravelh/archive/2011/04/13/2014417.html