File.Delete(Path);

DirectoryInfo di = new DirectoryInfo("指定目录");

判断目录是否存在

FileInfo[] fi = di.getFiles();//获得目录下文件

for(FileInfo f in fi){　

//判断指定文件是否存在

如果存在

File.Delete(f.FullName);　

}

给你两个函数实现： protected void delfile()
    {
        string filepath = Server.MapPath("~\\upfiles\\"); //upfiles 为指定的文件夹  你也可以写成变量进行替换
        ArrayList files =getAllDir(filepath);
        for (int i = 0; i < files.Count; i++)
        {
            FileInfo ofile = new FileInfo(filepath + files[i]);
            if (ofile.Exists)
            {
                try
                {
                    ofile.Delete();
                }
                catch
                {
                     Response.Write("<script>alert('删除出错！');                }
            }
        }
    }

 public static ArrayList getAllDir(string path)
    {
        ArrayList urlAddr = new ArrayList();//临时存放路径的链表
        if (Directory.Exists(path))
        {
            string[] fileList = Directory.GetFileSystemEntries(path);
            urlAddr.Clear();
            foreach (string file in fileList)
            {
                string newStr = Path.GetFullPath(file);
                string filename = Path.GetFileName(file);
                string strExtension = Path.GetExtension(newStr).ToLower();
                if (strExtension == ".xml")
                {
                    urlAddr.Add(filename);
                }
            }
        }
        return urlAddr;
    }