1.被flash挡住
设置flash的参数：<param name="wmode" value="opaque">
<object classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,29,0" width="468" height="60"><param name="movie" value="http://pepsi.flash8.net/pepsi46860.swf">
<param name="wmode" value="opaque"><param name="quality" value="high"><embed src="http://www.iyit.net/files/beyondpic/2006-5/27/0652709180916818.swf" quality="high" pluginspage="http://www.macromedia.com/go/getflashplayer" type="application/x-shockwave-flash" width="468" height="60"></embed></object>
<div style="position:absolute;left:150;top:50;width:100px;height:50px;background:green">
</div>
或者用<param name="wmode" value="transparent">
<object classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,29,0" width="468" height="60"><param name="movie" value="http://pepsi.flash8.net/pepsi46860.swf">
<param name="wmode" value="transparent"><param name="quality" value="high"><embed src="http://www.iyit.net/files/beyondpic/2006-5/27/0652709180916818.swf" quality="high" pluginspage="http://www.macromedia.com/go/getflashplayer" type="application/x-shockwave-flash" width="468" height="60"></embed></object>
<div style="position:absolute;left:150;top:50;width:100px;height:50px;background:green">
</div>
2.被图片挡住
这个估计是因为图片也放在层中，而图片所在层的z轴索引值比该层大，所以被挡住，解决办法是更改该层的z轴索引值至比图片层大。
<div style="position:absolute;left:0;top:20;z-index:2;background:red;width:120px;height:70px">
1<img src="http://www.iyit.net/files/beyondpic/2006-5/27/0652709181221473.gif">
</div>
<div style="position:absolute;left:50;top:50;z-index:2;background:green;width:120px;height:70px">
2<img src="http://www.iyit.net/files/beyondpic/2006-5/27/0652709181221473.gif">
</div>
<div style="position:absolute;left:90;top:80;z-index:2;background:blue;width:120px;height:70px">
3<img src="http://www.iyit.net/files/beyondpic/2006-5/27/0652709181221473.gif">
</div>
3.被表单控件挡住
这个目前还没有完美的解决方法，一般都是在设计排版时就尽量避免这种情况，如果是万不得已，就在层经过表单控件时让表单控件隐藏，过后再让它显示：
<button onclick="oselect.style.display='none';olayer.style.display='inline'">显示层隐藏下拉选项</button><button onclick="oselect.style.display='inline';olayer.style.display='none'">显示下拉选项隐藏层</button>

<div style="position:absolute;left:0;top:50;z-index:2;background:red;width:120px;height:50px">
z-index:1<select id="oselect"></select>
</div>
<div id="olayer" style="position:absolute;left:30;top:60;z-index:2;background:green;width:120px;height:70px;display:none">
z-index:2<img src="http://www.iyit.net/files/beyondpic/2006-5/27/0652709181221473.gif">
</div>
当然还有用优先级别较高的控件来代替层的方法解决，但控件并非是每台机器上都有安装，而且控件的可定制性也差，也就是常说的兼容性问题：
hhctrl.ocx
<object id=hhctrl type="application/x-oleobject" classid="clsid:adb880a6-d8ff-11cf-9377-00aa003b7a11" codebase="<i>file:</i>hhctrl.ocx#version=4,0,0,24" width=80 height=20>
<param name="command" value="related topics, menu">
<param name="button" value="menu">
<param name="item1" value="[x-eyes];http://x-lover.com/forums/">
<param name="item2" value="闪客之吧;http://www.flash8.net">
<param name="item3" value="零刻联盟;http://www.linkmeng.com/">
<param name="item4" value="蓝色理想;http://www.blueidea.com/">
<param name="item5" value="<a href="http://www.5d.cn">5d多媒体</a>;http://www.5d.cn">
</object>
<select></select>
window.createpopup()窗口(需要ie5.5+支持)
<script>
var opopup = window.createpopup();
function showpopupwin(){
var opopbody = opopup.document.body;
opopbody.style.backgroundcolor = "green";
opopup.show(50, 120, 180, 65,document.body);
}
</script>
<button onclick="showpopupwin()">click me!</button><select></select>
<iframe src="index.asp"></iframe>