Multi-serial ports are widely used in microcontrolled application systems. A highly （efficient）multi-serial port extension method based on ST16C554 and CPLD was presented in this （paper.） Its implementation is able to make four serial ports share one limited interrupt resource and thus reduce the system cost. ST16C554 works in FIFO mode, receives and transmits data by （interrupt）mode with a 16 byte hardware transmit buffer, that will also greatly cut down the load on the CPU.