<iframe src="XXX.htm" width="700px" frameborder="0" id="frmsrc" scrolling="no" marginheight="0" onload="AutoIframe()"></iframe>

<script type="text/javascript">
    function AutoIframe()
    {
        if(document.readyState!='complete')
        {
            setTimeout( function(){AutoIframe();},25 );
            return;
        }
        else
        {
           var ifobj=document.getElementById("frmsrc");
           ifobj.height= ifobj.contentWindow.document.body.scrollHeight;
        }
    }
</script>

//PS: XXX.htm不可跨域

<iframe src="dd.html" id="frmMain" name="frmMain" width="99%" height="100%" frameborder=0 scrolling=no marginHeight=0 marginWidth=0 onload="Javascript:SetWinHeight(this)" ></iframe>

function SetWinHeight(obj)
{
 var win=obj;
 if (document.getElementById)
 {
    if (win && !window.opera)
    {
  if (win.contentDocument && win.contentDocument.body.offsetHeight)
    win.height = win.contentDocument.body.offsetHeight;
  else if(win.Document && win.Document.body.scrollHeight)
    win.height = win.Document.body.scrollHeight;
    }
 }
}