The brake system of the civil aircraft is an important subsystem of the aircraft. During emergency braking, the accumulator provides hydraulic pressure to the brake. In addition, the brake accumulator provides continuous braking force when the aircraft is parked on the hangar or tarmac. Therefore, the brake accumulator plays an important role in the safety and operation of the aircraft. Because aircraft weight is so important, it is necessary to reduce the weight of the brake accumulator while ensuring its proper functioning. The material and structure of the brake accumulator are relatively mature. Reducing the size of the brake accumulator becomes a more feasible and effective means of reducing weight. This article takes a typical civil aircraft brake system as an example to study the optimization of the brake accumulator size.