Abstract: In order to realize the four-quadrant operation and speed control of small and micro DC motor, the PWM speed control system based on ARM chip and embedded operating system μC/OS-II control is designed. By adjusting the duty cycle of PWM signal and using the switch MOS tube to control the circuit, the forward and reverse rotation and speed control of the motor are realized. The protection circuit is set up by using the comparator and amplifier. The working principle, hardware realization, PWM driving circuit, control software design method and safety protection of the control system are introduced in detail. The long-term operation results of the system show that the PWM speed control system for DC motor has good working performance and achieves the expected design objectives.