The air-cooled motor controller has been widely used in electric aircraft due to its simple heat dissipation structure and maintenance-free features. Being the main heating component of the electric propulsion system of electric aircraft, the weight and the volume of the air-cooled motor controller need to be strictly controlled. Due to the short power running time of the electric motor controller, there is a large weight and volume allowance margin for the air-cooled radiatorbased on the rated power and heat dissipation requirements of the motor controller.This paper proposes an air-cooled radiator design method that can reduce its volume and weight by optimizing its structure based on the operating conditions of the electric aircraft under the heat dissipation requirements.The structure of the air-cooled motor can be optimized by optimizing the structure the minimum structure of the motor controller radiator constrained by the maximum temperature of the Insulated Gate Bipolar Transistor (IGBT) module,which can be determined using an algorithm called the motor controller thermal resistance network model. Experimental results obtained from a prototype test on a two-seat electric aircraft demonstrate the effectiveness of the optimization method. The air-cooled radiator designed using the proposed method can be reduced by 5% in weight while meeting the heat dissipation requirements of the motor controller of the electric aircraft.