思路：
1、首先设置ul里面的图片一共8张：ul.innerHTML+=ul.innerHTML
2、计算ul的实际宽度：ul.style.width = li[0].offsetWidth *li.length +'px'
3、
代码如下:
<!DOCTYPE html> <html> <head> <title>无缝滚动</title> <meta charset="utf-8"/> <style type="text/css"> *{ padding: 0px; margin: 0px; } .main{ width: 1200px; height: 200px; margin: 50px auto; position: relative; overflow: hidden; } ul{ list-style: none; position: absolute; top:0px; left: 0px; overflow: hidden; } ul li{ width: 300px; float: left; } </style> </head> <body> <div class="main"> <ul> <li> <img src="img/11.jpg" width="100%"> </li> <li> <img src="img/22.jpg" width="100%"> </li> <li> <img src="img/33.jpg" width="100%"> </li> <li> <img src="img/44.jpg" width="100%"> </li> </ul> </div> </body> <script type="text/javascript"> var div = document.querySelector('.main'); var ul = document.querySelector('ul'); var li = document.getElementsByTagName('li'); var speed = -2; ul.innerHTML +=ul.innerHTML; ul.style.width = li[0].offsetWidth*li.length +'px'; var timer = setInterval(move,30); function move(){ if (Number(ul.style.left) < -ul.offsetWidth/2) { ul.style.left = '0'; }else if (ul.offsetLeft >0) { ul.style.left = -ul.offsetWidth/2 +'px'; } ul.style.left = ul.offsetLeft + speed +'px'; } div.onmouseover = function(){ clearInterval(timer); } div.onmouseout = function(){ timer = setInterval(move,30); speed = 2; } </script> </html>