using ICSharpCode.SharpZipLib.Zip;
using ICSharpCode.SharpZipLib.Core;
using ICSharpCode.SharpZipLib.Checksums;

string zipPath = @"C:\Users\Cano\Desktop\api\test\百度手机卫士.zip";//要追加文件的压缩包地址
            string enName = "success.txt";//要在压缩包中添加的文件名
            byte[] bytes = Encoding.ASCII.GetBytes("a test file congratulation!");
            ZipFile zF1 = new ZipFile(zipPath);//可以看出 原本没有我要添加的entry
            ZipEntry zen2 = zF1.GetEntry(enName);
            zF1.Close();
            try {
                using (ZipOutputStream outStream = new ZipOutputStream(File.Open(zipPath, FileMode.Append))) {
                    ZipEntry newEntry = new ZipEntry(enName);
                    outStream.PutNextEntry(newEntry);
                    outStream.Write(bytes, 0, bytes.Length);//62501104
                    outStream.CloseEntry();
                }

                ZipFile zF = new ZipFile(zipPath);
                ZipEntry zen = zF.GetEntry(enName);//这里证明了我已经添加了entry  但是压缩包中并没有这个文件,解压的时候还提示"有额外的数据"
                zF.Close();
            }
            catch (Exception ex) {
                MessageBox.Show(ex.Message);
            }