Serial port is a common interface in Windows CE embedded operating system, Driver program of serial port is the bridge to link operating system and hardware. It adopts the scheme of, driver program of serial port,which combines the layered driver with stream driver. More description of key technologies on driver program is given, including register configuration, interrupt processing, implementation of function in MDD and PDD layer. The intention of this paper is to offer design method to driver program of embedded equipment in Windows CE.