老外那里找了个方法.可以做到覆盖select,但是必须指定高和宽,对动态支持不是很好.

Javascript:

function DivSetVisible(picPath, state) {
  var divRef = document.getElementById('PopupDiv');
  var IfrRef = document.getElementById('DivShim');
  var imgRef = document.getElementById('TopicPic');
  if (state) {
    divRef.style.display = "block";
    IfrRef.style.width = divRef.offsetWidth; IfrRef.style.height = divRef.offsetHeight;
    IfrRef.style.top = divRef.style.top;
    IfrRef.style.left = divRef.style.left;
    IfrRef.style.zIndex = divRef.style.zIndex - 1;
    IfrRef.style.display = "block";
  } else {
    divRef.style.display = "none"; IfrRef.style.display = "none";
  }
  imgRef.src = picPath;
} 

html:

<div id="PopupDiv" style="text-align: center; position: absolute; top: 110px; left: 15px; padding: 4px; display: none; background: #ff9; border: 1px solid #333; z-index: 100" onclick="DivSetVisible('', false);">
    <img id="TopicPic" alt="点击关闭" src="" />
  </div>
  <iframe id="DivShim" src="javascript:false;" scrolling="no" frameborder="0" style="position: absolute; top: 0px; left: 0px; display: none;"></iframe>