index.html:
<div style="height: 200px;"></div> <iframe id="gys" src="con.html" width="100%"></iframe>
con.html
<body onload="parent.window.document.all.gys.height=document.body.scrollHeight">
<div style="height: 1800px; width: 500px; margin: 0 auto; "></div>
</body>
ok了.
原文：http://www.cnblogs.com/guoyansi19900907/p/4329442.html