能过ChilkatDotNet4.dll组件，开发SFTP，上传下载功能。

 /// <summary>
    /// SFTP文件上传下载
    /// </summary>
    public class SFtp
    {
        /// <summary>
        /// http://www.example-code.com/csharp/sftp_readDir.asp
        /// </summary>
        Chilkat.SFtp sftp = new Chilkat.SFtp(); 
        /// <summary>
        /// 连接
        /// </summary>
        /// <returns></returns>
        public bool Connection()
        {  
            //尝试连接2次
            int tryCount = 0;
            while (tryCount++ < 2)
            {
                bool conn = TryConnection();
                if (conn == true)
                    return true;
            }
            return false;
        }

        /// <summary>
        /// 尝试连接
        /// </summary>
        /// <returns></returns>
        private bool TryConnection()
        {
            bool success = false;
            sftp.ConnectTimeoutMs = 1000;
            sftp.IdleTimeoutMs = 5000;
            //  Any string automatically begins a fully-functional 30-day trial. 
            success = sftp.UnlockComponent(AppConfig.GetValueByKey("sftpKey"));
            if (success != true)
            {
                LogHelper.Write("SFTP-----------注册失败！\r\n{0}", sftp.LastErrorText);
                return false;
            }

            //  Connect to the SSH server.
            //  The standard SSH port = 22
            //  The hostname may be a hostname or IP address. 
            string hostname = AppConfig.GetValueByKey("host");
            int port = Convert.ToInt32(AppConfig.GetValueByKey("port"));
            success = sftp.Connect(hostname, port);
            if (success != true)
            {
                LogHelper.Write("SFTP-----------服务拒绝连接！\r\n{0}", sftp.LastErrorText);
                return false;
            }
            string username = AppConfig.GetValueByKey("username");
            string pwd = AppConfig.GetValueByKey("pwd");
            success = sftp.AuthenticatePw(username, pwd);
            if (success != true)
            {
                LogHelper.Write("SFTP-----------服务名或密码错误！\r\n{0}", sftp.LastErrorText);
                return false;
            }
            //After authenticating, the SFTP subsystem must be initialized:
            success = sftp.InitializeSftp();
            if (success != true)
            {
                LogHelper.Write("SFTP----------- initialized Faile！\r\n{0}", sftp.LastErrorText);
                return false;
            }
            return success;
        }

       /// <summary>
       /// 创建目录
       /// </summary>
       /// <param name="folder">要创建的远程目录 eg:./aa/cc</param>
        public void MakeDirectory(string folder)
        {
            try
            {
                sftp.CreateDir(folder);
            }
            catch (Exception ex)
            {
                Log.LogHelper.Write("SFTP创建目录------------------ {0}", ex.ToString());
            }
        }

        /// <summary>
        /// 断开连接
        /// </summary>
        public void DisConnection()
        {
            try
            {
                if (sftp != null)
                {
                    sftp.Disconnect();
                }
            }
            catch (Exception ex)
            {
                Log.LogHelper.Write("SFTP关闭连接------------------ {0}", ex.ToString());
            }
        }

       
        /// <summary>
        /// 下载文件
        /// </summary>
        /// <param name="remoteFilePath">远程文件路径 eg: ./aa/hamlet.xml</param>
        /// <param name="localFilePath">本地文件路径  eg: c:/temp/hamlet.xml</param> 
        public bool DownFile(string remoteFilePath, string localFilePath)
        {
            bool success = false; 
            //  Note: The remote filepath may be an absolute filepath,
            //  a relative filepath, or simply a filename.
            //  Relative filepaths are always relative to the home directory
            //  of the SFTP/SSH user account.  There is no such thing
            //  as "current remote directory" in the SFTP protocol.
            //  A filename with no path implies that the file is located
            //  in the SFTP user account's home directory.  
            success = sftp.DownloadFileByName(remoteFilePath, localFilePath); 
            if (success != true)
            {
                LogHelper.Write("SFTP-----------文件下载\r\n{0}", sftp.LastErrorText); 
            } 
            return success;
        }

        /// <summary>
        /// 下载文件
        /// </summary>
        /// <param name="remoteFilePath">远程文件路径 eg: ./aa/hamlet.xml</param> 
        private void Rename(string remoteFilePath)
        {
            bool success = false; 
            //  Rename the file or directory:
            success = sftp.RenameFileOrDir(remoteFilePath + ".bak", remoteFilePath);
            if (success != true)
            {
                LogHelper.Write("SFTP-----------文件改名称\r\n名称是否已存在或{0}", sftp.LastErrorText); 
            }
        }

        /// <summary>
        /// 下载文件
        /// </summary>
        /// <param name="remoteFilePath">远程文件路径 eg: ./aa/hamlet.xml</param>
        /// <param name="localFilePath">本地文件路径  eg: c:/temp/hamlet.xml</param>
        /// <param name="remoteBakFilePath">远程备份目录 eg: ./ddd</param>
        public bool DownFileAndBak(string remoteFilePath, string localFilePath,string remoteBakFilePath)
        { 
            //下载
            if (DownFile(remoteFilePath, localFilePath))
            {
                //备份：上传
                if (UpLoadFile(remoteBakFilePath, localFilePath,false))
                {
                    //删除原件
                    if (DeleteFile(remoteFilePath))
                    {
                        return true;
                    }
                }
            }
            return false;
        }
         
        /// <summary>
        /// 文件上传
        /// </summary>
        /// <param name="remoteFilePath">远程文件路径 eg: ./aa/hamlet.xml</param>
        /// <param name="localFilePath">本地文件路径  eg: c:/temp/hamlet.xml</param>
        /// <returns></returns>
        public bool UpLoadFile(string remoteFilePath, string localFilePath, bool bAppendBak)
        {  
            bool success = false;
            string tmpRemoteFilePath = remoteFilePath;
            if (bAppendBak)
            {
                tmpRemoteFilePath += ".bak";
            }
            success = sftp.UploadFileByName(tmpRemoteFilePath, localFilePath);
            if (success != true)
            {
                LogHelper.Write("SFTP-----------上传文件\r\n{0}", sftp.LastErrorText); 
            }
            if (success && bAppendBak)
            {
                Rename(remoteFilePath);
            }
            return success;
        }
          
        /// <summary>
        /// 删除远程文件
        /// </summary>
        /// <param name="remoteFilePath">远程文件路径 eg: ./aa/hamlet.xml</param>
        /// <returns></returns>
        public bool DeleteFile(string remoteFilePath)
        {
            //  Delete a file on the server:
            bool success = false;
            success = sftp.RemoveFile(remoteFilePath);
            if (success != true)
            { 
                LogHelper.Write("SFTP-----------删除文件\r\n{0}", sftp.LastErrorText); 
            }
            return success;
        }

        /// <summary>
        /// 删除远程文件
        /// </summary>
        /// <param name="remoteFilePath">远程目录路径 eg: ./ddd</param>
        /// <returns></returns>
        public bool DeleteDir(string remoteDirPath)
        { 
            //  Delete a file on the server:
            bool success = false;
            success = sftp.RemoveDir(remoteDirPath);
            if (success != true)
            {
                LogHelper.Write("SFTP-----------删除文件\r\n{0}", sftp.LastErrorText);
            }
            return success;
        }

        /// <summary>
        /// 读取远程目录内所有文件
        /// </summary>
        /// <param name="remoteDirName">远程文件路径 eg: ./ddd</param>
        /// <returns></returns>
        private List<string> GetAllFileNames(string remoteDirName)
        {
            List<string> list = new List<string>();
            bool success = false;
            string handle;
            handle = sftp.OpenDir(remoteDirName);
            if (handle == null)
            {
                LogHelper.Write("SFTP-----------读取目录所有文件\r\n{0}", sftp.LastErrorText);
                return null;
            } 
            //  Download the directory listing:
            Chilkat.SFtpDir dirListing = null;
            dirListing = sftp.ReadDir(handle);
            if (dirListing == null)
            {
                LogHelper.Write("SFTP-----------读取目录所有文件\r\n{0}", sftp.LastErrorText);
                return null;
            }  
            int n = dirListing.NumFilesAndDirs;
            for (int i = 0; i <= n - 1; i++)
            {
                Chilkat.SFtpFile fileObj = null;
                fileObj = dirListing.GetFileObject(i);
                switch (fileObj.FileType)
                {
                    case "directory":
                        break;
                    case "regular":
                        if (System.Text.RegularExpressions.Regex.IsMatch(fileObj.Filename, AppConfig.GetValueByKey("ext")))
                        list.Add(fileObj.Filename); 
                        break;
                } 
            }  
            //  Close the directory
            success = sftp.CloseHandle(handle);
            if (success != true)
            {
                LogHelper.Write("SFTP-----------读取目录所有文件\r\n{0}", sftp.LastErrorText);
                return null;
            }
            return list;
        }

       /// <summary>
        /// 收取指定文件夹下所有文件
       /// </summary>
        /// <param name="remoteDirName">远程目录路径 eg: ./ddd</param>
        /// <param name="localDirName">本地目录路径 eg: D:/ddd</param>
        /// <param name="remoteBakFilePath">远程备份目录 eg: ./ddd</param>
        public List<string> DownAllFilesByDirName(string remoteDirName,string localDirName,string remoteBakFilePath = null)
        { 
            List<string> list = GetAllFileNames(remoteDirName);
            List<string> lsRetuen = new List<string>();
            if (list != null)
            {
                foreach (string s in list)
                {
                    if (string.IsNullOrEmpty("DownFileAndBak"))
                    {
                        if (DownFile(remoteDirName + "/" + s, localDirName + "/" + s))
                        { 
                            lsRetuen.Add(s);
                        }
                    }
                    else
                    {
                        if (DownFileAndBak(remoteDirName + "/" + s, localDirName + "/" + s, remoteBakFilePath + "/" + s))
                        {
                            lsRetuen.Add(s);
                        }
                    }
                }
            }
            return lsRetuen;
        }
    }