typedef struct _CANFRAME {
        UCHAR    mFrame[10];
    }CANFRAME,*PCANFRAME;

[DllImport("你的DLL路径")]
public static extern int Pci6621_Send(int mDev, int mPort, byte[] pSendFrame);

------解决方案--------------------

需要一个CANFRAME结构的指针（引用）
C# code
        [StructLayout(LayoutKind.Sequential)]
        public struct CANFRAME
        {
            [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.U1, SizeConst = 10)]
            public byte[] mFrame;
        }

        public class LibWrap
        {
            [DllImport("MyDll.dll")]
            public static extern bool Pci6621_Send([In] Int32 mDev, [In] Int32 mPort, ref CANFRAME pSendFrame);
        }


        static void Main()
        {
            CANFRAME sendFrame = new CANFRAME();
            sendFrame.mFrame = new byte[10];
            //sendFrame.mFrame[0] = 0x01;
            //...

            bool bSuccess = LibWrap.Pci6621_Send(0, 0, ref sendFrame);
        }

------解决方案--------------------

楼上办法可行，给你一个更全面的：

    http://blog.csdn.net/sdl2005lyx/article/details/6801113

------解决方案--------------------
ref 结构体名
结构体自己定义