Abstract: In view of problems of slow running speed, inflexible software programming existed in motor soft starter for belt conveyor and shredder because of taking 8 or 16 bits single-chip microcomputer as microprocessor, a soft starter based on STM32 and CPLD was designed. The starter adopts STM32F103C8T63 as intelligent control core and CPLD as assistant control core, generates a corresponding output information according to feedback information of voltage detection, current detection and external input device, and uses drive circuit to control trigger angle of three sets of inverse parallel thyristors to change motor starting voltage or frequency, so as to control the motor starting. The experimental results show that the soft starter overcomes disadvantage of big transient current of direct starting of motor, which has a good effect for improving start features of asynchronous motor.