/// <summary>

        /// 普通文件下载

        /// </summary>

        /// <param name="URL"></param>

        /// <param name="filename"></param>

        /// <returns></returns>

        public static bool DownloadFile(string URL, string filename)

        {

            try

            {

                HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(URL);

                HttpWebResponse webResponse = (HttpWebResponse)webRequest.GetResponse();

                Stream netFs = webResponse.GetResponseStream();

                Stream fs = new FileStream(filename,FileMode.Create);

                byte[] by = new byte[1024];

                int osize = netFs.Read(by, 0, (int)by.Length);

                while (osize > 0)

                {

                    fs.Write(by, 0, osize);

                    osize = netFs.Read(by, 0, (int)by.Length);

                }

                fs.Close();

                netFs.Close();

                webResponse.Close();

                webRequest.Abort();

                return true;

            }

            catch (System.Exception e)

            {

                System.Console.WriteLine(e.ToString());

                return false;

            }

        }

 /// <summary>

        /// 断点传输

        /// </summary>

        /// <param name="URL"></param>

        /// <param name="filename"></param>

        /// <returns></returns>

        public static bool DownloadFile2(string URL, string filename)

        {

            StringBuilder progress = new StringBuilder();

            int httpStatusCode = 200;

            //打开上次下载的文件或新建文件

            long lStartPos = 0;

            FileStream fs;

            if (File.Exists(filename))//另外如果文件已经下载完毕，就不需要再断点续传了，不然请求的range 会不合法会抛出异常。

            {

                fs = File.OpenWrite(filename);

                lStartPos = fs.Length;

                fs.Seek(lStartPos, SeekOrigin.Current); //移动文件流中的当前指针

            }

            else

            {

                fs = new FileStream(filename, FileMode.Create);

                lStartPos = 0;

            }

            try

            {

                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(URL);

                if (lStartPos > 0)

                {

                    request.AddRange((int)lStartPos); //设置Range值

                }

                WebResponse response = request.GetResponse();

                //向服务器请求，获得服务器回应数据流

                Stream netFs = response.GetResponseStream();

                long totalSize = response.ContentLength;

                Console.WriteLine($"totalsize:{totalSize / 1024 / 1024}MB"); // 从lStartPos位置开始读获得的大小

                long hasDownSize = 0;

                byte[] nbytes = new byte[512];//521,2048 etc

                int nReadSize = 0;

                nReadSize = netFs.Read(nbytes, 0, nbytes.Length);

                while (nReadSize > 0)

                {

                    progress.Clear();

                    fs.Write(nbytes, 0, nReadSize);

                    nReadSize = netFs.Read(nbytes, 0, nbytes.Length);

                    hasDownSize += nReadSize;

                    //progress.Append("("+(((double)hasDownSize * 100 / totalSize).ToString("0.00")) + " %)");

                    //Console.WriteLine(progress);

                }

                fs.Close();

                netFs.Close();

                return true;

            }

            catch (WebException ex)

            {

                var rsp = ex.Response as HttpWebResponse;

                httpStatusCode = (int)rsp.StatusCode;

                fs.Close();

                if (httpStatusCode == 416)  //request.AddRange((int)lStartPos) 超出范围

                {

                    Console.WriteLine("文件均下载完成");

                    return true;

                }

                else

                {

                    Console.WriteLine("下载过程中出现错误:" + ex.ToString());

                    return false;

                }

            }

        }

使用例子：

DownloadFile2("http://localhost//file//Windows Kits.rar", "Windows Kits.rar");