<asp:FileUpload ID="FileUpload1" onchange="selectFolder(event)" webkitdirectory mozdirectory msdirectory odirectory directory AllowMultiple="true" runat="server" />

要么

<input type="file" id="FileUpload" onchange="selectFolder(event)" webkitdirectory mozdirectory msdirectory odirectory directory multiple />

JavaScript的：

<script type="text/javascript">
function selectFolder(e) {
    var theFiles = e.target.files;
    var relativePath = theFiles[0].webkitRelativePath;
    var folder = relativePath.split("/");
    alert(folder[0]);
}
</script>