public Boolean ValidateDomainUser(string Domain, string UserName, string Password)

        {

            DirectoryEntry entry = new DirectoryEntry(Domain, UserName, Password);

            try

            {

                string objectSid = (new SecurityIdentifier((byte[])entry.Properties["objectSid"].Value, ).Value);//如果账号不对则会抛出异常

                return true;

            }

            catch

            {

                return false;

            }

            finally

            {

                entry.Dispose();

            }

        }

//代码调用，LDAP一定要大写。

MessageBox.Show(ValidateDomainUser("LDAP://域控的IP地址/DC=ha-ad,DC=net", "evan", "evan的密码").ToString());