The maintainability of civil aircraft directly affects market competitiveness and is one of the key factors for the successful operation of civil aircraft.The maintainability prediction is one of the main tasks in the civil aircraft development process,which can evaluate whether the design meets maintainability requirements.As one of the methods of maintainability prediction, sampling scoring method has the advantages of small sample size, simple prediction and can be used in the initial stage of design.The power system supplies power to all electrical equipment of the aircraft, and its maintainability directly affects the normal operation of the airborne equipment, and plays a key role in the maintainability design of the whole aircraft.This paper studies on the sampling scoring method, and according to the current status of civil aircraft maintainability design, quantifies the human factor rating checklist for the maintenance requirements.and the sampling scoring method is optimized. In this paper, the maintainability of the electrical power system of a certain aircraft type was estimated by sampling scoring method, and whether it meets the maintainability design requirements is evaluated.Finally, the importance of sampling scoring method in the process of civil aircraft maintenance design was expounded.