How to develop Virtual x Driver(VxD) in windows system bottom layer is given to realize high efficiency interrupt communication of serial port. By analyzing Virtual x Driver, Programable Interrupt Controller, how to virtually a interruption is proposed. With the operational principle of UART chip 8250, the communication of serial port is analyzed. Finally, the communication between WIN32 application and VxD is discussed, and the constitute of the VxD is given. The applied solid example expresses that method of the serial port communication is efficient.