var ScrollMiddle = {
     'Odiv':document.getElementById('comment'), // 目標DOM    
     'Oli': document.getElementById('comment').getElementsByTagName('li'), 
     'times':30,      // 配置滾動時間                        
     'delay':1000,    // 配置暫停的時間                
     inint:function(){
       this.size = this.Oli.length;
       this.height = 59;
       this.countHeight =this.size * this.height;
       this.Odiv.innerHTML+=this.Odiv.innerHTML;
       this.timer = null;
     },
     scroll:function(){
       var _this = this;
       _this.inint();
       function scrolls(){

         var scrollValue = _this.Odiv.scrollTop;
         var sub_timer = null;
         var num=0;
         if(scrollValue>=_this.countHeight){
           _this.Odiv.scrollTop = 0;
         }else{
           _this.Odiv.scrollTop++;
           if(scrollValue%_this.height==0){
             clearInterval(_this.timer)
             function delay(){
               num++;
               if(num==3){
                 num=0;
                 clearInterval(sub_timer);
                 sub_timer = null;
                 clearInterval(_this.timer)
                 _this.timer = setInterval(scrolls,_this.times);
                 return false;
               }
             }
             sub_timer = setInterval(delay,_this.delay)
           }
         }
       }
       this.timer = setInterval(scrolls,_this.times);
     }
   }

<ul id="comment">
  <li></li>
  ......
</ul>

#comment{
  width:200px;
  height:200px;
  overflow:hidden;  
}