using Ionic.Zip;

if (!Page.IsPostBack)
{
    Response.Clear();
    Response.BufferOutput = false;
    string[] files = Directory.GetFiles(Server.MapPath("img/"));
    //网站文件生成一个readme.txt文件
    String readmeText = String.Format("README.TXT" +Environment.NewLine+
                                "官方地址：http://shandongit.com"
                                );
    Response.ContentType = "application/zip";
    Response.AddHeader("content-disposition", "inline; filename=\"" + String.Format("archive-{0}.zip", DateTime.Now.ToString("yyyy-MMM-dd-HHmmss")) + "\"");
    //批量压缩操作
    using (ZipFile zip = new ZipFile())
    {
        // the Readme.txt file will not be password-protected.
        zip.AddEntry("Readme.txt", readmeText, Encoding.Default);
        zip.Password = "shandongit.com";
        zip.Encryption = EncryptionAlgorithm.WinZipAes256;

        // filesToInclude is a string[] or List<String>
        zip.AddFiles(files, "files");

        zip.Save(Response.OutputStream);

    }
    Response.Close();
}