Abstract: The paper analyzed problems existed in realizing pulse width modulation of intelligent control system of vibration stress relief which includes short timing time of the single-chip microcomputer, method of initial value writing of the timer and low frequency accuracy, and gave corresponding solutions. It proposed basic idea of using single-chip microcomputer to realize pulse width modulation: timers of the single-chip microcomputer are timed respectively at high level and low level to make common I/O interface output pulse with constant frequency or variable frequency and constant width. The Proteus and Keil C joint simulation results show that the design method of pulse width modulation of intelligent control system of vibration stress relief can output pulse signal meeting the requirements.