Abstract: The work takes a new liquid-cooling plate in a power battery with pin fins inside the channel as the object. A mathematical model is established via the central composite design of the response surface to study the relationships among the length, width, height, and spacing of pin fins; the maximum temperature and temperature difference of the battery module; and the pressure drop of the liquid-cooling plate. Model accuracy is verified via variance analysis. The new liquid-cooling plate enables the power battery to work within an optimal temperature range. Appropriately increasing the length, width, and height and reducing the spacing of pin fins could reduce the temperature of the power battery module and improve the temperature uniformity. However, the pressure drop of the liquid-cooling plate increases. The structural parameters of the pin fins are optimized to minimize the maximum temperature and the temperature difference of the battery module as well as the pressure drop of the liquid-cooling plate. The errors between the values predicted and actual by the simulation test are 0.58%, 4%, and 0.48%, respectively, which further verifies the model accuracy. The results reveal the influence of the structural parameters of the pin fins inside the liquid-cooling plate on its heat dissipation performance and pressure drop characteristics. A theoretical basis is provided for the design of liquid-cooling plates in power batteries and the optimization of structural parameters.