如果你使用的是。net Framework 4.0，这很简单:

Environment.Is64BitOperatingSystem

看到环境。Is64BitOperatingSystem属性。

. net 4在环境类中有两个新属性，Is64BitProcess和Is64BitOperatingSystem。有趣的是，如果你使用Reflector，你会发现它们在32位和64位版本的mscorlib中实现的不同。32位版本为Is64BitProcess返回false，并通过P/Invoke为Is64BitOperatingSystem调用IsWow64Process。64位版本对两者都返回true。

最快的方式:

if(IntPtr.Size == 8) {
    // 64 bit machine
} else if(IntPtr.Size == 4)  {
    // 32 bit machine
} 

注意:这是非常直接的，只有当程序不强制作为32位进程执行时(例如，在项目设置中通过<Prefer32Bit>true</Prefer32Bit>)，才能在64位上正确工作。

微软为此提供了一个代码示例:

http://1code.codeplex.com/SourceControl/changeset/view/39074#842775

它是这样的:

    /// <summary>
    /// The function determines whether the current operating system is a 
    /// 64-bit operating system.
    /// </summary>
    /// <returns>
    /// The function returns true if the operating system is 64-bit; 
    /// otherwise, it returns false.
    /// </returns>
    public static bool Is64BitOperatingSystem()
    {
        if (IntPtr.Size == 8)  // 64-bit programs run only on Win64
        {
            return true;
        }
        else  // 32-bit programs run on both 32-bit and 64-bit Windows
        {
            // Detect whether the current process is a 32-bit process 
            // running on a 64-bit system.
            bool flag;
            return ((DoesWin32MethodExist("kernel32.dll", "IsWow64Process") &&
                IsWow64Process(GetCurrentProcess(), out flag)) && flag);
        }
    }

    /// <summary>
    /// The function determins whether a method exists in the export 
    /// table of a certain module.
    /// </summary>
    /// <param name="moduleName">The name of the module</param>
    /// <param name="methodName">The name of the method</param>
    /// <returns>
    /// The function returns true if the method specified by methodName 
    /// exists in the export table of the module specified by moduleName.
    /// </returns>
    static bool DoesWin32MethodExist(string moduleName, string methodName)
    {
        IntPtr moduleHandle = GetModuleHandle(moduleName);
        if (moduleHandle == IntPtr.Zero)
        {
            return false;
        }
        return (GetProcAddress(moduleHandle, methodName) != IntPtr.Zero);
    }

    [DllImport("kernel32.dll")]
    static extern IntPtr GetCurrentProcess();

    [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
    static extern IntPtr GetModuleHandle(string moduleName);

    [DllImport("kernel32", CharSet = CharSet.Auto, SetLastError = true)]
    static extern IntPtr GetProcAddress(IntPtr hModule,
        [MarshalAs(UnmanagedType.LPStr)]string procName);

    [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool IsWow64Process(IntPtr hProcess, out bool wow64Process);

还有一个可用的WMI版本(用于测试远程机器)。

对不起，是VB的代码。NET，但是很容易移植到c#。 它可以在Win7, x64和.Net Framework 4.8上正常工作:

Dim r As String = ""
Using searcher As ManagementObjectSearcher = New System.Management.ManagementObjectSearcher("SELECT * FROM Win32_OperatingSystem")
    Dim Information As ManagementObjectCollection = searcher.Get()
    If Information IsNot Nothing Then
        For Each obj As ManagementObject In Information
            r = obj("Caption").ToString() & _
            " - " & _
            obj("OSArchitecture").ToString() ' <--- !!! "64-bit" shown here
        Next
    End If
    MessageBox.Show(r)
End Using

使用此命令获取已安装的Windows体系结构:

string getOSArchitecture()
{
    string architectureStr;
    if (Directory.Exists(Environment.GetFolderPath(
                           Environment.SpecialFolder.ProgramFilesX86))) {
        architectureStr ="64-bit";
    }
    else {
        architectureStr = "32-bit";
    }
    return architectureStr;
}