<SCRIPT LANGUAGE="JavaScript">
function sc1(){
 document.getElementById("Div1").style.top=(document.documentElement.scrollTop+(document.documentElement.clientHeight-document.getElementById("Div1").offsetHeight)/2)+"px";
 document.getElementById("Div1").style.left=(document.documentElement.scrollLeft+(document.documentElement.clientWidth-document.getElementById("Div1").offsetWidth)/2)+"px";

document.getElementById("Div1").style.position:="absolute";

}
</SCRIPT>

 

window.onscroll=sc1();  //滾動(dòng)條事件

 

<div id="Div1" class="div" style="width: 240px; height:90px" align="center">正中...</div>

 

主要的代碼 都是上面的了！