In this paper, the cooling performance of the battery thermal management system (BTMS) was optimized based on the Z-type parallel air cooling model and the computational fluid dynamics (CFD) method. Firstly, the effects of the distributed and convergent plenum angle on the cooling performance of the battery pack were analyzed. An air cooling BTMS experimental system was designed to verify the reliability of the CFD method. The results indicated that the DP with an angle had a positive impact on the heat dissipation performance of the BTMS. Next, the DP was divided into eight parts according to the number of batteries, and the angle of each part of DP was optimized respectively. Compared with the original model, the maximum temperature (T-max) and maximum temperature difference (Delta T-max) of the optimal model were decreased by 3.81 K (7.50%) and 5.64 K (90.97%), respectively. Furthermore, the influence of the length and height of the manifolds on the heat dissipation effect was studied. Then, the cooling performances of the battery pack were optimized by adjusting the widths of the cooling channels and adding a spoiler in the cooling channel. Compared with the initial model, T-max and Delta T-max of the optimal condition were decreased by 5.37 K (10.57%) and 5.74 K (92.58%), respectively. And the pressure drop was increased by 16.12 Pa, but it was within an acceptable range. Finally, the effects of different wind speeds and discharge rates on the cooling effect were discussed. The proposed thermal management method in this paper would provide a reference for designing a battery air cooling system in the future. Novelty Statement The cooling performance of the battery thermal management system (BTMS) was optimized based on the Z-type parallel air cooling model and the computational fluid dynamics (CFD) method. The optimization strategy of discussing DP angle in sections was proposed, which could accurately control the temperature of each battery. An air-cooled BTMS experimental system was designed to verify the reliability of the CFD method.