Temperature of lithium-ion battery has a huge impact on battery life and performance. Thus, it is important to properly manage the battery cooling system to maintain target battery temperature. In this paper, a numerical model for battery pack and its cooling system for battery electric vehicle(BEV) is developed. In this model, battery stack of 50 kWh capacity is cooled by coolant flow through the fin-assisted cooling plate. The model calculate the temperature change of battery stack under several design and operation factors. Predicted battery life is suggested according to the simulation results.