<script src="jquery.js" type="text/javascript" charset="gb2312"></script>
<script type="text/javascript">
$(window).scroll( function(){
var height=$("#yc").offset().top-$(window).scrollTop();
if(height<"50"){
$(".guding").css("display","none");
}else{
$(".guding").css("display","block");
}
});
</script>
<div class="guding" style="position:fixed; background:red;height:50px;z-index:10; top:0;width:100%;">A:这个DIV是固定的</div>
<div style="position:relative; margin-top:200px; background:rgb(245,245,245);height:1000px; width:100%;" id="yc">B:滚动到这里的时候隐藏</div>
