In the butanol production by liquid fermentation of straw, in order to achieve highefficiency fermentation, the distribution of the bacteria in the fermentation liquid should be uniform, and the added materials needed to be stirred in time. Due to the large size of the fermenter for industrial production of butanol, the agitation process required a higher output torque of the drive motor. Therefore, a straw fermenter with high efficiency, small volume, low speed and high torque was of great significance for the industrial fermentation of butanol. A statorrotor permanent magnet vernier motor was designed for fermentation liquid agitation. The specific selection of the slotpole combinations of the motor and the electromagnetic performance were studied. A prototype was built and hysteresis control was used to achieve rapid response to liquid fermentation objects, enabling a lowenergy and efficient fermentation process.