var adjustIframe = function (id) {
    var iframe = document.getElementById(id)
    var idoc = iframe.contentWindow && iframe.contentWindow.document || iframe.contentDocument;
    var callback = function () {
        var iheight = Math.max(idoc.body.scrollHeight, idoc.documentElement.scrollHeight); //取得其高
        iframe.style.height = iheight + "px";
    }
    if (iframe.attachEvent) {
        iframe.attachEvent("onload", callback);
    } else {
        iframe.onload = callback
    }
}

HTML代码如下所示： 

<iframe id="js_sub_web" width="80%" frameborder="0" scrolling="no" allowTransparency="true" src="http://www.cnblogs.com/rubylouvre/archive/2009/09/15/1566722.html">
</iframe>

window.onload = function(){
     adjustIframe("js_sub_web");
}