不废话，看代码
<script type="text/javascript">
function changeFrameHW(){
var ifm= document.getElementById("ifr");
ifm.height=document.documentElement.clientHeight;
ifm.width=document.documentElement.clientWidth;
}
window.onresize=function(){
changeFrameHW();
}
</script><iframe id="ifr" src="http://www.baidu.com" scrolling="no" onload="changeFrameHW()" frameborder="0"></iframe>