首先引入jQuery
js代码如下
$(function(){
        //当滚动条的位置处于距顶部100像素以下时，跳转链接出现，否则消失
        $(function () {
            $(window).scroll(function(){
                if ($(window).scrollTop()>100){
                    $("#backtop").css("bottom","1px");
                }
                else
                {
                    $("#backtop").css("bottom","-100px");
                }
            });

            //当点击跳转链接后，回到页面顶部位置
            $("#backtop").click(function(){
                //$('body,html').animate({scrollTop:0},1000);
        if ($('html').scrollTop()) {
                $('html').animate({ scrollTop: 0 }, 1000);
                return false;
            }
            $('body').animate({ scrollTop: 0 }, 1000);
                 return false;            
           });       
     });    
});

css

#backtop{position:fixed;right:7.5%;bottom:-100px;z-index:2;overflow:auto;width:54px;height:54px;border-top-right-radius:50px;border-top-left-radius:50px;background-image:url(btt.png);background-position:0 0;cursor:pointer;-webkit-transition:all .5s ease-in-out;-moz-transition:all .5s ease-in-out;-o-transition:all .5s ease-in-out;transition:all .5s ease-in-out;-ms-transition:all .5s ease-in-out}

html

<div id="backtop" title="返回顶部" style="bottom: -100px;"></div>

图片素材