string path = System.Windows.Forms.Application.StartupPath+"\\1.jpg";//下载到的地址+文件名
?????????????????
???????????????????// 设置参数
???????????????????HttpWebRequest request = WebRequest.Create("http://172.31.2.7:3480/resource/root/服务券/生日礼/10月/twg160922_392x120.jpg") as HttpWebRequest;
???????????????????//发送请求并获取相应回应数据
???????????????????HttpWebResponse response = request.GetResponse() as HttpWebResponse;
???????????????????//直到request.GetResponse()程序才开始向目标网页发送Post请求
???????????????????Stream responseStream = response.GetResponseStream();
???????????????????//创建本地文件写入流
???????????????????Stream stream = new FileStream(path, FileMode.Create);
???????????????????byte[] bArr = new byte[1024];
???????????????????int size = responseStream.Read(bArr, 0, (int)bArr.Length);
???????????????????while (size > 0)
???????????????????{
???????????????????????stream.Write(bArr, 0, size);
???????????????????????size = responseStream.Read(bArr, 0, (int)bArr.Length);
???????????????????}
???????????????????stream.Close();
???????????????????responseStream.Close();
net ??根据连接地址下载文件，图片
原文地址：http://www.cnblogs.com/zengwangjing/p/7649904.html