.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://www.163design.net/a/s/"http://pepsi.flash8.net/pepsi46860.swf">
<param name="wmode" value="opaque"><param name="quality" value="high"><embed src=http://www.163design.net/a/s/"http://pepsi.flash8.net/pepsi46860.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://www.163design.net/a/s/"http://pepsi.flash8.net/pepsi46860.swf">
<param name="wmode" value="transparent"><param name="quality" value="high"><embed src=http://www.163design.net/a/s/"http://pepsi.flash8.net/pepsi46860.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.163design.net/a/s/"http://www.flash8.net/images/logo.gif">
</div>
<div style="position:absolute;left:50;top:50;z-index:2;background:green;width:120px;height:70px">
2<img src=http://www.163design.net/a/s/"http://www.flash8.net/images/logo.gif">
</div>
<div style="position:absolute;left:90;top:80;z-index:2;background:blue;width:120px;height:70px">
3<img src=http://www.163design.net/a/s/"http://www.flash8.net/images/logo.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.163design.net/a/s/"http://www.flash8.net/images/logo.gif">
</div>