<frameset rows="*" cols="1215,*" framespacing="0" frameborder="yes" border="0"> 
<frame src="popScreenLeft.htm" name="leftFrame" scrolling="NO" > 
  <frame src="popScreenRight_new.htm" name="mainFrame"　scrolling="NO"> 
</frameset>
<script>
var locations=["popScreenLeft.htm"，"popScreenLeft1.htm"，"popScreenLeft3.htm"];
var index=0;
var TIMER;
function changeperten(){
   leftFrame.location.herf=locations[index++];
   TIMER=setTimeout(changeperten,10000);
}
window.onload=function(){
   TIMER=setTimeout(changeperten,10000);
}
</script>

------解决方案--------------------
改一下10秒
HTML code

<script language="javascript">
var n = 0;
var urls = ['popScreenLeft.htm','popScreenLeft1.htm','popScreenLeft3.htm'];
function doit(){
  leftFrame.location.href = urls[n] + "?" + escape(new Date());
  n++;
  if(n==3) n=0;
}
window.onload=function(){
    setInterval("doit()", 10000)
}
</script>
<frameset rows="*" cols="1215,*" framespacing="0" frameborder="yes" border="0"> 
<frame src="popScreenLeft.htm" name="leftFrame" scrolling="NO" > 
  <frame src="popScreenRight_new.htm" name="mainFrame"　scrolling="NO"> 
</frameset>