切勿尝试写二进制数据作为字符串，像你一样。这将无法正常工作。写的二进制数据作为二进制数据。您可以使用流为代替的StreamWriter 。

Never try to write binary data as strings, like you do. It won't work correctly. Write binary data as binary data. You can use Stream for that instead of StreamWriter.

using (Stream stream = new FileStream(fileName, FileMode.OpenOrCreate))
{
    stream.Seek(1000, SeekOrigin.Begin);
    stream.Write(Data, 0, Data.Length);
}