Abstract: Aerodynamic drag generated by high-speed train seriously impairs the operating economy of trains and restricts a further increase in speed. Currently, the drag reduction method with streamlined bodies has approached its limit. Meanwhile, the existence of external insulation equipment will increase the drag on the roof, and optimization of the external insulation equipment for drag reduction is an important development direction. However, the equipment also plays an essential role in electrical insulation, therefore, both aerodynamic characteristics and insulation performance need to be considered. In this paper, a dimple structure was constructed on the surface of the insulator shed to reduce the drag. The pit spacing, pit transverse and longitudinal axes, and pit depth were taken as variables, and the minimum drag coefficient was taken as the objective, so that the response values were calculated by using the Latin square sampling method to select samples to establish an approximate model. Then, a global optimization search using genetic algorithm was conducted to obtain the optimal parameters of the pit. Finally, dry flash and foul flash tests were conducted on the pit insulators to verify their insulation performance. The results show that the pit structure can achieve a maximum 15.62% resistance reduction of the roof insulator, and can increase the insulator dry flash voltage under certain airflow conditions to ensure its insulation performance. And when the insulator is contaminated, the pit insulator can also have good electrical insulation performance to ensure the safe operation of the train.