[HttpPost]
        public ActionResult Index(HttpPostedFileBase pic)
        {
            string fileFormat = Path.GetExtension(pic.FileName);
            string fileName = Guid.NewGuid().ToString("N");
            string imageSaveDirectory = Server.MapPath("~/Upload");

            if (!Directory.Exists(imageSaveDirectory))
            {
                Directory.CreateDirectory(imageSaveDirectory);
            }

            bool result = false;
            string imageSavePath = Path.Combine(imageSaveDirectory, fileName + fileFormat);
            pic.SaveAs(imageSavePath);
            if (System.IO.File.Exists(imageSavePath))
            {
                result = true;
            }

            //上传成功
            if (result)
            {
                return Json(new { result = "1", msg = "OK" });
            }
            else
            {
                //上传失败
                return Json(new { result = "0", msg = "Fail"});
            }
        }

我项目中的一些代码，也许有帮助。

[HttpPost]
        public ActionResult LEdit(Shop_MemberLevel _shop_MemberLevel, HttpPostedFileBase ImgPath)
        {
            _shopMemeber.UpdateLevel(_shop_MemberLevel, ImgPath);
            return SuccessMsg("AdminMemberMemberLevel");
        }

public void UpdateLevel(Shop_MemberLevel shopMemeberLevel, HttpPostedFileBase logoFile)
        {
            shopMemeberLevel.ImgPath = SaveImages(logoFile, new int[][] { new int[] { 100, 30 }, new int[] { 200, 10 }, }, "W",
                   "Download\\Level");
            _unitOfWork.Shop_MemberLevelRepository().Update(shopMemeberLevel);
            _unitOfWork.Save();
        }

 /// <summary>
        /// 保存图片以及生产缩略图
        /// </summary>
        /// <param name="imageFileBase">图片流</param>
        /// <param name="imageName">保存的图片名</param>
        /// <param name="sizes">缩略图大小，sizes为形如[ [width1,height1], [width2,height2] ]的数组</param>
        /// <param name="mode">生成缩略的模式，HW-拉伸，W-指定宽度，H-指定高度，Cut-剪裁</param>
        /// <param name="directory">目录，前后无斜杠</param>
        /// <returns>保存的文件夹路径</returns>
        public string SaveImages(HttpPostedFileBase imageFileBase, int[][] sizes, string mode, string directory = "")
        {
            //检查并创建目录
            string path = HttpContext.Current.Server.MapPath("/");
            string virtulpath = "";
            if (!string.IsNullOrEmpty(directory))
            {
                virtulpath += directory + "\\";
            }
            path += virtulpath;
            if (!Directory.Exists(path))
            {
                Directory.CreateDirectory(path);
            }

            //创建GUID
            var guid = Guid.NewGuid();

            //保存原图
            imageFileBase.SaveAs(path + guid + ".jpg");

            /*生成缩略图
             * sizes为形如
             * [ [width, height],[width2, height2]]
             *的二维数组 
             */

            foreach (int[] size in sizes)
            {
                if (size.Count() != 2)
                {
                    continue;
                }

                int width = size[0];
                int height = size[1];

                string thumPath = path + guid + "_" + width + "x" +
                                  height + ".jpg";
                MakeThumNail(path + guid + ".jpg", thumPath, width, height, mode);
            }
            return "\\" + virtulpath + guid + ".jpg";
        }

        /// <summary>
        /// 生成缩略图
        /// </summary>
        /// <param name="orginalImagePat">原图片地址</param>
        /// <param name="thumNailPath">缩略图地址</param>
        /// <param name="width">缩略图宽度</param>
        /// <param name="height">缩略图高度</param>
        /// <param name="model">生成缩略的模式，HW-拉伸，W-指定宽度，H-指定高度，Cut-剪裁</param>
        public void MakeThumNail(string originalImagePath, string thumNailPath, int width, int height, string model)
        {
            //originalImagePath = MapPath(originalImagePath);
            //thumNailPath = HttpContext.Current.Server.MapPath(thumNailPath);
            System.Drawing.Image originalImage = System.Drawing.Image.FromFile(originalImagePath);

            int thumWidth = width;      //缩略图的宽度
            int thumHeight = height;    //缩略图的高度

            int x = 0;
            int y = 0;

            int originalWidth = originalImage.Width;    //原始图片的宽度
            int originalHeight = originalImage.Height;  //原始图片的高度

            switch (model)
            {
                case "HW":      //指定高宽缩放,可能变形
                    break;
                case "W":       //指定宽度,高度按照比例缩放
                    thumHeight = originalImage.Height * width / originalImage.Width;
                    break;
                case "H":       //指定高度,宽度按照等比例缩放
                    thumWidth = originalImage.Width * height / originalImage.Height;
                    break;
                case "Cut":
                    if ((double)originalImage.Width / (double)originalImage.Height > (double)thumWidth / (double)thumHeight)
                    {
                        originalHeight = originalImage.Height;
                        originalWidth = originalImage.Height * thumWidth / thumHeight;
                        y = 0;
                        x = (originalImage.Width - originalWidth) / 2;
                    }
                    else
                    {
                        originalWidth = originalImage.Width;
                        originalHeight = originalWidth * height / thumWidth;
                        x = 0;
                        y = (originalImage.Height - originalHeight) / 2;
                    }
                    break;
                default:
                    break;
            }

            //新建一个bmp图片
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(thumWidth, thumHeight);

            //新建一个画板
            System.Drawing.Graphics graphic = System.Drawing.Graphics.FromImage(bitmap);

            //设置高质量查值法
            graphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

            //设置高质量，低速度呈现平滑程度
            graphic.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

            //清空画布并以透明背景色填充
            graphic.Clear(System.Drawing.Color.Transparent);

            //在指定位置并且按指定大小绘制原图片的指定部分
            graphic.DrawImage(originalImage, new System.Drawing.Rectangle(0, 0, thumWidth, thumHeight), new System.Drawing.Rectangle(x, y, originalWidth, originalHeight), System.Drawing.GraphicsUnit.Pixel);

            try
            {
                bitmap.Save(thumNailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
            }
            catch (Exception ex)
            {

                throw ex;
            }
            finally
            {
                originalImage.Dispose();
                bitmap.Dispose();
                graphic.Dispose();
            }

        }