在C#中，可以使用System.IO.Compression命名空間中的GZipStream類來實現gzip壓縮和解壓。下面是一個簡單的示例代碼：

using System;
using System.IO;
using System.IO.Compression;

public class GZipHelper
{
    public static void CompressFile(string sourceFile, string compressedFile)
    {
        using (FileStream sourceStream = new FileStream(sourceFile, FileMode.Open))
        {
            using (FileStream compressedStream = File.Create(compressedFile))
            {
                using (GZipStream compressor = new GZipStream(compressedStream, CompressionMode.Compress))
                {
                    sourceStream.CopyTo(compressor);
                }
            }
        }
    }

    public static void DecompressFile(string compressedFile, string decompressedFile)
    {
        using (FileStream compressedStream = new FileStream(compressedFile, FileMode.Open))
        {
            using (FileStream decompressedStream = File.Create(decompressedFile))
            {
                using (GZipStream decompressor = new GZipStream(compressedStream, CompressionMode.Decompress))
                {
                    decompressor.CopyTo(decompressedStream);
                }
            }
        }
    }
}

使用示例：

string sourceFile = "source.txt";
string compressedFile = "compressed.gz";
string decompressedFile = "decompressed.txt";

GZipHelper.CompressFile(sourceFile, compressedFile);
GZipHelper.DecompressFile(compressedFile, decompressedFile);

這樣就可以實現對文件進行gzip壓縮和解壓縮操作。