function IsWin64: Boolean;
var
  Kernel32Handle: THandle;
  IsWow64Process: function(Handle:THandle; var Res:BOOL):BOOL; stdcall;
  GetNativeSystemInfo: procedure(var lpSystemInfo: TSystemInfo); stdcall;
  isWoW64: Bool;
  SystemInfo: TSystemInfo;
  const
    PROCESSOR_ARCHITECTURE_AMD64 = 9;
    PROCESSOR_ARCHITECTURE_IA64 = 6;
begin
  Kernel32Handle := GetModuleHandle('KERNEL32.DLL');
  if Kernel32Handle = 0 then
    Kernel32Handle := LoadLibrary('KERNEL32.DLL');
  if Kernel32Handle <> 0 then
  begin
    IsWOW64Process := GetProcAddress(Kernel32Handle,'IsWow64Process');
    //需要注意是GetNativeSystemInfo 函数从Windows XP 开始才有，
    //而 IsWow64Process 函数从 Windows XP with SP2 以及 Windows Server 2003 with SP1 开始才有。
    //所以使用该函数的时候最好用GetProcAddress 。
    GetNativeSystemInfo := GetProcAddress(Kernel32Handle,'GetNativeSystemInfo');
    if Assigned(IsWow64Process) then
    begin
      IsWow64Process(GetCurrentProcess,isWoW64);
      Result := isWoW64 and Assigned(GetNativeSystemInfo);
      if Result then
      begin
        GetNativeSystemInfo(SystemInfo);
        Result := (SystemInfo.wProcessorArchitecture = PROCESSOR_ARCHITECTURE_AMD64) or
                  (SystemInfo.wProcessorArchitecture = PROCESSOR_ARCHITECTURE_IA64);
      end;
    end
    else
      Result := False;
  end
  else
    Result := False;
end;

http://blog.csdn.net/risesoft2012/article/details/51260830