[HttpPost]

        public FileResult ExportCSV()

        {

            var apps =。。。。//linq以及EF从数据库查询数据

            MemoryStream ms = new MemoryStream();

            StreamWriter sw = new StreamWriter(ms);

            var csv = new CsvWriter(sw);

            foreach (var pp in apps)

            {

                csv.WriteField();      //set to '0'

                csv.WriteField("");     //set empty space

                csv.WriteField("haha");

                csv.NextRecord();

            }

            sw.Flush();

            ms.Position = ;

            return File(ms, "text/comma-separated-values", "Export.csv");

        }    

@using (Html.BeginForm("ImportCSV", "ExportImport", FormMethod.Post, new { enctype = "multipart/form-data" }))

{

    <div class="row  row-margin">

        <div class="col-lg-4">

            <div class="form-group">

                <input type="file" name="csvToUpload" id="csvToUpload" accept=".csv">

            </div>

        </div>

        <div class="col-lg-6"></div>

        <div class="col-lg-2 pull-right">

            <button type="submit" class="btn btn-default btn-space-right btn-space-left"><span class="glyphicon glyphicon-import"></span> Import</button>

            <button type="button" class="btn btn-default pull-right" onclick="backHomePage();"><span class="glyphicon glyphicon-step-backward"></span> Quit</button>

        </div>

    </div>

}

        [HttpPost]

        public JsonResult ImportCSV(HttpPostedFileBase csvToUpload)

        {

                    using (var textReader = new StreamReader(csvToUpload.InputStream))

                    {

                        var csv = new CsvReader(textReader);

                        while (csv.Read())

                        {

                            var field = csv.GetField<string>();

                        }

                    }

            .......

        }