List<FileSystemRights> ret = new List<FileSystemRights>();

            DirectorySecurity dirSec = Directory.GetAccessControl(@"c:\test", AccessControlSections.All);
            AuthorizationRuleCollection rules = dirSec.GetAccessRules(true, true, typeof(System.Security.Principal.NTAccount));
            foreach (FileSystemAccessRule rule in rules)
            {
                ret.Add(rule.FileSystemRights);
            }

ret里面就是各个帐号对该目录的访问权限，你在里面判断一下就知道了，格式是这样的：
ReadData | WriteData | AppendData | ReadExtendedAttributes | WriteExtendedAttributes | ExecuteFile | DeleteSubdirectoriesAndFiles | ReadAttributes | WriteAttributes | Delete | ReadPermissions | ChangePermissions | TakeOwnership | Synchronize

 **********************************

判断在该文件夹下面有没有创建文件的权限

using System;
using System.IO;
using System.Security.AccessControl;

namespace FileSystemExample
{
    class DirectoryExample
    {
        public static void Main()
        {
            try
            {
                string DirectoryName = "TestDirectory";

                Console.WriteLine("Adding access control entry for " + DirectoryName);

                // Add the access control entry to the directory.
                AddDirectorySecurity(DirectoryName, @"MYDOMAIN\MyAccount", FileSystemRights.ReadData, AccessControlType.Allow);

                Console.WriteLine("Removing access control entry from " + DirectoryName);

                // Remove the access control entry from the directory.
                RemoveDirectorySecurity(DirectoryName, @"MYDOMAIN\MyAccount", FileSystemRights.ReadData, AccessControlType.Allow);

                Console.WriteLine("Done.");
            }
            catch (Exception e)
            {
                Console.WriteLine(e);
            }

            Console.ReadLine();
        }

        // Adds an ACL entry on the specified directory for the specified account.
        public static void AddDirectorySecurity(string FileName, string Account, FileSystemRights Rights, AccessControlType ControlType)
        {
            // Create a new DirectoryInfo object.
            DirectoryInfo dInfo = new DirectoryInfo(FileName);

            // Get a DirectorySecurity object that represents the
            // current security settings.
            DirectorySecurity dSecurity = dInfo.GetAccessControl();

            // Add the FileSystemAccessRule to the security settings.
            dSecurity.AddAccessRule(new FileSystemAccessRule(Account,
                                                            Rights,
                                                            ControlType));

            // Set the new access settings.
            dInfo.SetAccessControl(dSecurity);

        }

        // Removes an ACL entry on the specified directory for the specified account.
        public static void RemoveDirectorySecurity(string FileName, string Account, FileSystemRights Rights, AccessControlType ControlType)
        {
            // Create a new DirectoryInfo object.
            DirectoryInfo dInfo = new DirectoryInfo(FileName);

            // Get a DirectorySecurity object that represents the
            // current security settings.
            DirectorySecurity dSecurity = dInfo.GetAccessControl();

            // Add the FileSystemAccessRule to the security settings.
            dSecurity.RemoveAccessRule(new FileSystemAccessRule(Account,
                                                            Rights,
                                                            ControlType));

            // Set the new access settings.
            dInfo.SetAccessControl(dSecurity);

        }
    }
}