In order to meet the mileage requirements of new energy vehicles, it is necessary to improve the capacity of power batteries. Therefore, this paper proposes a new optimization method of energy storage capacity of power batteries of new energy vehicles based on fuzzy control. Firstly, according to the control block diagram of power battery, the fuzzy control method is used to control the power of power battery, and the relationship between the sum of power fluctuation out of limit and the change of battery rated energy storage capacity is obtained. Secondly, the objective function of energy storage capacity optimization of new energy vehicle power battery is constructed, and the constraints of energy storage capacity optimization of new energy vehicle power battery are constructed based on the constraints of battery charge and discharge power and SOC. The optimization of energy storage capacity can be realized by solving the objective function under constraints. Finally, a comparative verification experiment is carried out. The experimental results show that this method can effectively control the power fluctuation of power battery and improve the energy storage capacity of battery.