js:

<script>

//固定表头开始
$(document).ready(function(){
     dh_fd();
});
functiondh_fd(){
   var   hight = document.body.scrollHeight;
         hight = hight-0;
   if($(window).scrollTop() >= 120 && $(window).scrollTop()<=hight ){

       $(".xx_dh_fd").show();

   }else{

       $(".xx_dh_fd").hide();
   }
}
functionTop() {
     $("html, body").animate({scrollTop : 0 }, 120);
}
$(window).scroll(function() {dh_fd();});
$(window).resize(function(){dh_fd();});
//固定表头结束

</script>

样式:
.xx_dh_fd{
   background:#ffffff;
   left:auto;top:0px;
   display:none;
   position:fixed;z-index:9999999;
   width:98%;
   _position:absolute;/*IE6*/
   _width:98%;/*IE6*/

}

加一个需要隐藏的表头
//固定的表头
<tabale id="id1" class="xx_dh_fd"><tabel>
//要固定的表头
<tabale id="id2"><tabel>