Polymer electrolyte fuel cell (PEFC) needs to be examined relative humidity distribution and current density distribution to improve the durability. In this study, the PEFC reaction and thermal flow analysis model including the effect of cooling water was developed. Furthermore, the effects of the shape of separator channels and the flow pattern on current density distribution and relative humidity distribution were examined by this numerical analysis. As a result, it was found that the uniform current density distribution did not directly relate to the uniform humidity distribution, because the humidity distribution was complexly affected by the generated water, the water transfer between the anode and the cathode and the gas temperature. Moreover, it was confirmed that the optimal flow pattern of gas and cooling water could make the relative humidity higher and more uniform. This calculation model can help us to design the optimal separator shape and to determine the optimal operating conditions which can narrow the low humidity area and improve the cell durability. (c) 2006 Elsevier B.V. All rights reserved.