Lithium-ion battery pack is widely used in electric vehicles (EVs), for which reasonable heat dissipation measures must be taken to keep battery working in a suitable temperature range. Liquid cooling is popular for its efficient heat dissipation performance. In order to evaluate the effect of layout and channel design of cooling plates on the heat dissipation of a battery module, numerical modeling and analyses were carried out. Two arrangements of the cooling plates with different coolant channels (i.e., single channel, multiple small channels, and S-shaped channel) are discussed. The Z-score method is applied to evaluate the six cooling plate designs with various inlet flow rates. It is found that the design with two cooling plates sandwiching one battery module shows a better cooling performance. In terms of the channel structures, the comprehensive performance of the cooling plates with multiple small flow channels is optimal, when inlet flow rate is between 7.817 × 10−4 kg s−1 ∼ 0.0105 kg s−1 under the New European Driving Cycle (NEDC) condition.