In order to keep the power battery work within an ideal temperature range for the electric vehicle, the liquid cooling plate with parallel multi-channels is designed, and a three-dimensional thermal model of battery module with the liquid cooling plate is established. Subsequently, the effects of the cooling plate thickness and the cooling pipe thickness, channel number and coolant mass flow rate on the cooling performance of battery modules are analyzed. The results show that four parameters of the cooling plate have an important role in the thermal behavior of the liquid-cooled battery system. It is not good to improve the performance of the cooling system by changing only certain parameters. The four factors discussed above are optimized by using orthogonal test according to the univariate analysis. With the use of the orthogonal test, the optimization model obtained is obviously enhanced in the aspect of maximum temperature control and temperature uniformity of liquid-cooled battery module. Results show that the three-dimensional thermal analysis and orthogonal test method are compatible with optimal design of liquid-cooled battery modules.