代码如下：

<span id="t_d">00天</span><span id="t_h">00时</span><span id="t_m">00分</span><span id="t_s">00秒</span>
<script type="text/javascript">
function getRTime(){
	var EndTime= new Date('2017/12/12 00:00:00');//截止时间
	var NowTime = new Date();
	var t =EndTime.getTime() - NowTime.getTime();
	var d=Math.floor(t/1000/60/60/24);
	var h=Math.floor(t/1000/60/60%24);
	var m=Math.floor(t/1000/60%60);
	var s=Math.floor(t/1000%60);
	document.getElementById("t_d").innerHTML = d + "天";
	document.getElementById("t_h").innerHTML = h + "时";
	document.getElementById("t_m").innerHTML = m + "分";
	document.getElementById("t_s").innerHTML = s + "秒";
}
setInterval(getRTime,1000);
</script>