Understanding the cold start process of polymer electrolyte fuel cell (PEFC) is crucial to the development of an advanced PEFC of good cold start performance or to the design of advanced cold start strategies. In this study, a three‐dimensional cold start model has been adapted and further developed to numerically investigate the cold start behavior under the applied clamping pressure, which was not considered in previous cold start modeling and simulation work. The PEFC cold start performance is studied under various assembly pressures in terms of polarization curves, ice formation, water content profile, and current density distribution, etc. The results indicate that, using a large clamping pressure leads to a significant decline on the cold start performance; therefore, using an optimum clamping pressure is important to obtain a better cold start performance. It is found that increasing the clamping pressure not only increases the ice accumulation in cathode catalyst layer, but also causes the dehydration of membrane and decreases the cold start performance. The proposed model can be used as a powerful tool to study the realistic cold start performance of PEFC and to assist the development of more advanced PEFC cold start strategies.