The utility model provides a device used for preventing a stator from deforming for a motor. At least two through holes penetrated with a plurality of punching sheets are arranged on the stator consisting of the punching sheets which are laminated with each other, the through holes are uniformly disposed outside an effective outer-diameter area of the stator, and key steel for preventing the stator from deforming is arranged in each through hole. The device is added onto the stator of the small and medium-sized motor, and after the periphery of the stator is welded, the key steel is punched into the periphery of the stator, thereby being capable of effecting increasing the strength of the stator and preventing the stator from deforming. After the device is added onto the stator, a motor base can be omitted while the strength of the stator is guaranteed, so that the stator is more attractive in appearance and simpler in structure. The device can be applied to the field of small and medium-sized motors well, is simple in manufacturing method which requires only punching holes on an original stator structure and punching the key steel in the holes, is simple and easy in manufacturing process, and does not affect the original structure of the motor.