复制代码 代码如下:

#topmenu{position:absolute;top:100px;background:#4b4a4a;width:100%;margin:0 auto;clear:both;overflow:hidden;z-index:998;left:0}

<script type="text/javascript">

jQuery(document).ready(function() {

var topmenu = jQuery("#topmenu");

var topmenu_top = topmenu.offset().top;

reset_topmenu_top(topmenu, topmenu_top);

jQuery(window).scroll(function() {

reset_topmenu_top(topmenu, topmenu_top);

});

});

function reset_topmenu_top(topmenu, topmenu_top) {

var document_scroll_top = jQuery(document).scrollTop();

if (document_scroll_top > topmenu_top) {

topmenu.css('top', document_scroll_top);

}

if (document_scroll_top <= topmenu_top) {

topmenu.css('top', topmenu_top);

}

}

</script>

效果图如下：