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;
}

完整的答案是这样的(摘自stefan-mg, ripper234和BobbyShaftoe的答案):

    [DllImport("kernel32.dll", SetLastError = true, CallingConvention = CallingConvention.Winapi)]
    [return: MarshalAs(UnmanagedType.Bool)]
    public static extern bool IsWow64Process([In] IntPtr hProcess, [Out] out bool lpSystemInfo);

    private bool Is64Bit()
    {
        if (IntPtr.Size == 8 || (IntPtr.Size == 4 && Is32BitProcessOn64BitProcessor()))
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    private bool Is32BitProcessOn64BitProcessor()
    {
        bool retVal;

        IsWow64Process(Process.GetCurrentProcess().Handle, out retVal);

        return retVal;
    } 

首先检查您是否处于64位进程中。如果不是，检查32位进程是否是Wow64Process。

这只是Bruno Lopez上面建议的一个实现，但适用于Win2k +所有的WinXP服务包。我只是想把它贴出来这样别人就不用亲手卷了。(本可以作为评论发布，但我是一个新用户!)

[DllImport("kernel32", SetLastError = true, CallingConvention = CallingConvention.Winapi)]
public extern static IntPtr LoadLibrary(string libraryName);

[DllImport("kernel32", SetLastError = true, CallingConvention = CallingConvention.Winapi)]
public extern static IntPtr GetProcAddress(IntPtr hwnd, string procedureName);

private delegate bool IsWow64ProcessDelegate([In] IntPtr handle, [Out] out bool isWow64Process);

public static bool IsOS64Bit()
{
    if (IntPtr.Size == 8 || (IntPtr.Size == 4 && Is32BitProcessOn64BitProcessor()))
    {
        return true;
    }
    else
    {
        return false;
    }
}

private static IsWow64ProcessDelegate GetIsWow64ProcessDelegate()
{
  IntPtr handle = LoadLibrary("kernel32");

  if ( handle != IntPtr.Zero)
  {
    IntPtr fnPtr = GetProcAddress(handle, "IsWow64Process");

    if (fnPtr != IntPtr.Zero)
    {
      return (IsWow64ProcessDelegate)Marshal.GetDelegateForFunctionPointer((IntPtr)fnPtr, typeof(IsWow64ProcessDelegate));
    }
  }

  return null;
}

private static bool Is32BitProcessOn64BitProcessor()
{
  IsWow64ProcessDelegate fnDelegate = GetIsWow64ProcessDelegate();

  if (fnDelegate == null)
  {
    return false;
  }

  bool isWow64;
  bool retVal = fnDelegate.Invoke(Process.GetCurrentProcess().Handle, out isWow64);

  if (retVal == false)
  {
    return false;
  }

  return isWow64;
}

下面是c#中使用DllImport的直接方法。

[DllImport("kernel32.dll", SetLastError = true, CallingConvention = CallingConvention.Winapi)] 
[return: MarshalAs(UnmanagedType.Bool)] 
public static extern bool IsWow64Process([In] IntPtr hProcess, [Out] out bool lpSystemInfo); 

public static bool Is64Bit() 
{ 
    bool retVal; 

    IsWow64Process(Process.GetCurrentProcess().Handle, out retVal); 

    return retVal; 
} 

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)。

我在许多操作系统上都成功地使用了这个检查:

private bool Is64BitSystem
{
   get
   {
      return Directory.Exists(Environment.ExpandEnvironmentVariables(@"%windir%\SysWOW64"));
   }
}

不管操作系统的语言是什么，这个文件夹总是命名为“SysWOW64”。这适用于。net Framework 1.1或更高版本。