從ftp伺服器下載檔案步驟如下:

   1. 建立ftp物件, 連結FTP伺服器

       建立FtpWebRequest的物件 request, 並與ftp伺服器的檔案連結.

       using System.Net;

        FtpWebRequest request = FtpWebRequest.Create(FTPString) as FtpWebRequest;
        //  FTPString =  FTPAddress + "/" + filename
  

 2. 用userid和password登入ftp伺服器

            request.Method = WebRequestMethods.Ftp.DownloadFile;
            request.Credentials = new NetworkCredential(username, password);

             
   3. 將keepalive屬性設為True, 重複使用同一物件實體(instance) 

        request.KeepAlive = true;        ///執行後不要關閉連結
        request.UsePassive = true;       


   4. 使用binary方法傳送資料

        request.UseBinary = true;

   5. 將ftp檔案讀入buffer

        FtpWebResponse response = request.GetResponse() as FtpWebResponse;
        Stream reader = response.GetResponseStream();

        MemoryStream memStream = new MemoryStream();

        
         byte[] buffer = new byte[1024];    //每次讀取1024 bytes

         while (true)
         {
                Application.DoEvents();        

                int bytesRead = reader.Read(buffer, 0, buffer.Length);

                if (bytesRead == 0)
                {
                      //已經沒有資料, 結束下載
                       Application.DoEvents();
                       break;
                 }
                 else
                 {
                        //資料寫入buffer
                        memStream.Write(buffer, 0, bytesRead);

                  }
                }

                byte[] downloadedData = memStream.ToArray();

                reader.Close();
                memStream.Close();
                response.Close();

   6. 存檔     

      用filestream開啟本地磁碟機檔案, 並將檔案資料由 FileStream  

      FileStream newFile = new FileStream(saveFile1.FileName, FileMode.Create);
                        newFile.Write(downloadedData, 0, downloadedData.Length);
                        newFile.Close();

      FtpWebReguest物件的其他方法

       建立目錄
        FtpWebRequest Request = (FtpWebRequest)WebRequest.Create("ftp://IP address/Directory");
        Request.Credentials = new NetworkCredential("id", "pwd");
        Request.Method = WebRequestMethods.Ftp.MakeDirectory;
        FtpWebResponse Response = (FtpWebResponse)Request.GetResponse();
        Response.Close();

        修改檔案名稱
        FtpWebRequest Request = (FtpWebRequest)WebRequest.Create("ftp://IP address/FileName");
        Request.Credentials = new NetworkCredential("id", "pwd");
        Request.Method = WebRequestMethods.Ftp.Rename;
         Request.RenameTo = "NewFileName";
        FtpWebResponse Response = (FtpWebResponse)Request.GetResponse();
        Response.Close();

        移除檔案
        FtpWebRequest Request = (FtpWebRequest)WebRequest.Create  ("ftp://IP address/FileName");
        Request.Credentials = new NetworkCredential("id", "pwd");
        Request.Method = WebRequestMethods.Ftp.DeleteFile;
        FtpWebResponse Response = (FtpWebResponse)Request.GetResponse();
        Response.Close();

參考資料來源：

 C# FTP Upload

 C# Download File FTP