<iframe id="frame_con" src="bb.html" frameborder=0 scrolling=no style="margin-left:0px;margin-top:-3px;width:785px;height:550px;float:right;"></iframe>

//引入jQuery
<script src="http://res.func.fetionpictest.com/js/public/jquery-1.3.2.min.js?2011122701" type="text/javascript"></script>
<script type="text/javascript">
          //document.domain = "fx-func.com";//指向根域
         $(window.parent.document).find("#frame_con").load(function(){//绑定事件
         var main = $(window.parent.document).find("#frame_con");//找到iframe对象
         var thisheight = $(document).height()+30;//获取页面高度
         main.height(thisheight < 500 ? 500 : thisheight);
//为iframe高度赋值如果高度小于500，则等于500，反之不限高，自适应
                });
     </script>

$("#frame_con").load(function(){
    var thisheight = $(this).contents().find("body").height()+30;
    $(this).height(thisheight < 500 ? 500 : thisheight);
});