Good heat dissipation of Lithium battery can prevent the battery from shortening its life due to rapid aging or thermal runaway. In this paper, an air-cooled structure of 5 series and 3 parallel battery packs is designed, which combines the advantages of series and parallel air ducts and optimizes the heat dissipation effect and the space ratio of air ducts. First, the heat generation model of NCR18650PF lithium battery is established, and the heat generation rate and time under different discharge rates are calculated. Combined with the working conditions of the battery itself, the necessity of battery pack heat dissipation was found. Secondly, a preliminary three-dimensional model of the battery pack heat dissipation was established, and a simulation analysis was carried out to study the influence of the inclination angle of the inlet duct, the arrangement of the air inlet and outlet, and the influence of the deflector on the heat dissipation effect, and the optimization analysis was carried out step by step according to the simulation results. It is found that, under the premise of symmetrical arrangement of air inlet and outlet, the inlet duct inclination angle is set to 10°, which can achieve better economic efficiency with smaller model size and lower manufacturing cost. In addition, two deflectors in the center of the model and heat dissipation holes on both sides of the shell can achieve the best heat dissipation effect and minimize the temperature difference of battery discharge. Finally, when the room temperature is 298 K, the discharge rate is 2C, and the air inlet speed is 3 m/s, the maximum temperature of the battery pack is 305.34 K, which is 3.75 K lower than the series air duct and 2.78 K lower than the parallel air duct, while the temperature difference drops to 4.68 K compared with the conventional air duct, indicating that the overall temperature uniformity and heat dissipation of the battery pack with the heat dissipation structure designed in this paper is better.