Abstract: The microcontroller MC9S12DG128B of Freescale HCS12 was used as the main control chip of the trajectory tracking control system for model cars. The infrared photoelectric sensor detected the black guide line on the white runway. The direction of the car was controlled by rotating a steering gear. The closed loop control was realized for model carS through PID algorithm and speed. As a result, the exact path search and correct trajectory tracking were realized. Experiment showed that the operation of the system was stable and reliable.