The soft starter is widely used in the starting of three-phase cage asynchronous motors. Because of its small starting current and reduced damage to the grid and motor during the traditional start-up of the motor it is applied in industrial, agricultural and transportation. The starting current of the motor is controlled by intelligently controlling the firing angle of the thyristor to achieve soft start of the motor in this paper. Fuzzy control is added to the system to establish a control model, which enhances the error resistance of the entire system and enhances the robustness, thus continuously improving the entire system. Fuzzy control is applied in this system to control the constant current soft start of the motor, which greatly improves the intelligence of the motor. The system can reduce the starting current, improve its dynamic torque, can effectively suppress the influence of pure hysteresis. In a large number of experiments and practical production work, it can be proved that the fuzzy control system of motor based on PLC has very good stability, can effectively suppress the influence of pure lag, and indeed has very good control effect.