Abstract: Aiming at the problem of preventive maintenance of motorized spindle, firstly, the structure and common faults of motorized spindle are analyzed, and the fault prone parts and causes are obtained; Then, according to the fault prone parts of motorized spindle, the preventive maintenance system of motorized spindle is designed, the performance measurement scheme and evaluation standard of fault prone parts are designed, and the preventive maintenance method of motorized spindle is obtained; Finally, the preventive maintenance method is applied to a variety of precision CNC machine tool motorized spindle, and the effectiveness of the proposed preventive maintenance method is verified. The experimental results show that the proposed preventive maintenance method can effectively identify the early performance degradation of motorized spindle, and provide an effective basis for preventive maintenance and performance degradation trend monitoring.