你直接把
ftp = (FtpWebRequest)FtpWebRequest.Create(new Uri(“ftp：//123.12.12.12/aaa/bbb”));

private void DownloadImages(string localFolder, string remotPath, string fileName)
        {
            FtpWebRequest reqFTP;

            string ftpServerIP = ConfigurationManager.AppSettings[“FtpServer”];
            string ftpUserID = ConfigurationManager.AppSettings[“FtpUid”];
            string ftpPassword = ConfigurationManager.AppSettings[“FtpPwd”];
            string ftpPort = ConfigurationManager.AppSettings[“FtpPort”];

            try
            {
                FileStream outputStream = new FileStream(localFolder + “\” + fileName, FileMode.Create);

                reqFTP = (FtpWebRequest)FtpWebRequest.Create(new Uri(“ftp://” + ftpServerIP + “:” + ftpPort + “/” + remotPath + “/” + fileName));

                reqFTP.Method = WebRequestMethods.Ftp.DownloadFile;

                reqFTP.UseBinary = true;

                reqFTP.Credentials = new NetworkCredential(ftpUserID, ftpPassword);

                FtpWebResponse response = (FtpWebResponse)reqFTP.GetResponse();

                Stream ftpStream = response.GetResponseStream();

                long cl = response.ContentLength;

                int bufferSize = 2048;

                int readCount;

                byte[] buffer = new byte[bufferSize];

                readCount = ftpStream.Read(buffer, 0, bufferSize);

                while (readCount > 0)
                {
                    outputStream.Write(buffer, 0, readCount);

                    readCount = ftpStream.Read(buffer, 0, bufferSize);
                }

                ftpStream.Close();

                outputStream.Close();

                response.Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

//ftpServerIP 、ftpUserID 、ftpPassword、ftpPort  这些配置都写在App.config文件里
<?xml version=”1.0″ encoding=”utf-8″ ?>
<configuration>
  <appSettings>
    <add key=”FtpServer” value=”192.168.1.11″/>
    <add key=”FtpUid” value=”orms”/>
    <add key=”FtpPwd” value=”orms”/>
    <add key=”FtpPort” value=”22″/>
  </appSettings>
</configuration>

调用方法示例：

DownloadImages(@”d:\temp”, “ccc/ddd”, “test.jpg”);

引用

http://www.cnblogs.com/swtseaman/archive/2011/03/29/1998611.html

里面有一个GotoDirectory（）方法，直接调用
GotoDirectory(“aaa/bbb”,false)

好吧 各位 我自己也弄出来了，刚才debug的时候才弄明白的，解决的方法和你们说的差不多，谢谢啊

楼主后来怎么解决的？