The traditional AC motor speed control system can not effectively control the abnormal current output value, and the output current value after control has no periodic change rule. Therefore, an AC motor speed control system based on CFPWM is proposed. After the description of the system hardware and the selection of m051 chip, the equivalent circuit diagram of CFPWM operation is drawn, and on this basis, the speed control model of AC motor is designed. On this basis, the introduction of PID algorithm, combined with the ideal running state of AC motor, control model closed-loop speed regulation, completes the design of system function. In addition, through comparative experiments, it is proved that the designed system can effectively control the current output value of AC motor, and the output current value can be controlled within the effective range after the effective control of current.