用window.onscroll事件加scrollby
function FloatDiv()
{
     document.getElementById("Hid_ScrollTop").value = document.documentElement.scrollTop;
}
window.onscroll= FloatDiv;
function SetScrollPostion()
{
         var vScrollTop = document.getElementById("Hid_ScrollTop").value         if(vScrollTop != "")
         scrollBy(0,vScrollTop);
}
在onload事件里调用SetScrollPostion(),