1、使用IsOSPlatform()和OSDescription判断

使用System.Runtime.InteropServices.RuntimeInformation.IsOSPlatform()判断平台操作系统，参数包括：

OSPlatform.Windows
OSPlatform.OSX
OSPlatform.Linux

例如，

bool isWindows = System.Runtime.InteropServices.RuntimeInformation
                                               .IsOSPlatform(OSPlatform.Windows);
//使用OSDescription获取操作系统版本信息，如可能值为Microsoft Windows 10.0.10586
var osNameAndVersion = System.Runtime.InteropServices.RuntimeInformation.OSDescription;

2、通过系统环境变量判断

string windir = Environment.GetEnvironmentVariable("windir");
if (!string.IsNullOrEmpty(windir) && windir.Contains(@"\") && Directory.Exists(windir))
{
    _isWindows = true;
}
else if (File.Exists(@"/proc/sys/kernel/ostype"))
{
    string osType = File.ReadAllText(@"/proc/sys/kernel/ostype");
    if (osType.StartsWith("Linux", StringComparison.OrdinalIgnoreCase))
    {
        // Note: Android gets here too
        _isLinux = true;
    }
    else
    {
        throw new UnsupportedPlatformException(osType);
    }
}
else if (File.Exists(@"/System/Library/CoreServices/SystemVersion.plist"))
{
    // Note: iOS gets here too
    _isMacOsX = true;
}
else
{
    throw new UnsupportedPlatformException();
}