A simple mathematical model is developed to investigate the superiority of the interdigitated flow field design over the conventional one, especially in terms of maximum power density. Darcy＇s equation for porous media and the standard diffusion equation with effective diffusivity are used in the gas diffuser, and a coupled boundary condition given by the Butler-Volmer equation is used at the catalyst layer interface. The performance of PEM fuel cells with a conventional flow field and an interdigitated flow field is studied with other appropriate boundary conditions. The theoretical results show that the limiting current density of a fuel cell with an interdigitated flow field is about three times the current density of a fuel cell with a conventional flow field. The results also demonstrate that the interdigitated flow field design can double the maximum power density of a PEM fuel cell. The modelling results compared well with experimental data in the literature.