Presently, the feeding of the corn thresher is controlled artificially . The uneven feeding speed directly affects the life of machine and the degree of corn threshing. Meanwhile, the traditional corn threshers were designed basing on hitting principle, which would damage the corn grain significantly. In view of these factors, a kind of automatic control system which is based on STM32, is used to control the extrusion and rubbing on corn thresher.The system, controlled by STM32, achieves the automatic feeding through the stepper motor, accomplishes the corn threshing as well as the separation of grain corn and corn cob by screw extrusion, it adopts full automatic control. Simultaneously, it can effectively reduce the damage rate of corn grain, and improve corn threshing rate and the integrity of corn cob.