C#代码使用Uri类来计算相对路径

    public static string GetRelativePath(string fullPath, string basePath)
    {
        if (string.IsNullOrEmpty(fullPath)) throw new ArgumentNullException(nameof(fullPath));
        if (string.IsNullOrEmpty(basePath)) throw new ArgumentNullException(nameof(basePath));

        Uri fullUri = new Uri(fullPath);
        Uri baseUri = new Uri(basePath + Path.DirectorySeparatorChar);
        
        return Uri.UnescapeDataString(baseUri.MakeRelativeUri(fullUri).ToString())
            .Replace('/', Path.DirectorySeparatorChar);
    }

    static void Main()
    {
        string fullPath = @"D:\项目\红旗\拆装\images\AS5\AS05000RM.jpg";
        string basePath = @"D:\项目\红旗\拆装";
        
        Console.WriteLine(GetRelativePath(fullPath, basePath));
    }