<div class="fileupload">
    <a href="javascript:;" class="add_btn">添加附件</a>
    <div class="fileupload_div" onclick="upfile_click(this)">
        <asp:FileUpload ID="FileUpload1" runat="server" CssClass="fileupload_input"/>
    </div>
</div>
<style>
.fileupload{
    position:relative;
}
.fileupload_div{
    filter: alpha(opacity=0);
    -webkit-opacity:0;
    -moz-opacity:0;
    opacity:0;
    background-color:black;
    cursor:pointer;
    height:16px;
    left:0;
    overflow:hidden;
    position:absolute;
    top:0;
    width:72px;
    margin-left:10px;
}
.fileupload_input{
    filter: alpha(opacity=0);
    -webkit-opacity: 0;
    -moz-opacity: 0;
    position: absolute;
    top: 0;
    width: 100%;
    height: 100%;
    visibility: hidden;
}
</style>