CSS部分：

<style> .backToTop{display:none; width:18px; line-height:1.2; padding:5px 0; background-color:#000; color:#fff; font-size:12px; text-align:center; position:fixed; _position:absolute; right:10px; bottom:100px; _bottom:"auto"; cursor:pointer; opacity:.6; filter:Alpha(opacity=60);} </style>

JS部分：

<script> (function() {  

var $backToTopTxt = "返回顶部", $backToTopEle = $('<div class="backToTop"></div>').appendTo($("body"))  

 .text($backToTopTxt).attr("title", $backToTopTxt).click(function() {    $("html, body").animate({ scrollTop: 0 }, 120);

   }), $backToTopFun = function() {  

    var st = $(document).scrollTop(), winh = $(window).height();  

 (st > 0)? $backToTopEle.show(): $backToTopEle.hide();  

   //IE6下的定位

      if (!window.XMLHttpRequest) {    $backToTopEle.css("top", st + winh - 166);   

   }

  }; 

   $(window).bind("scroll", $backToTopFun);  

   $(function() { $backToTopFun(); }); })();

</script>