A pseudo-homogeneous model for cathode catalyst layer performance in PEM fuel cells is derived from a basic mass-current balance by the control volume approach. The model considers kinetics of oxygen reduction at the catalyst/electrolyte interface, proton transport through the polymer electrolyte and oxygen diffusion through porous voids. A relaxation method is developed to solve the governing equations, which belong to the two-point boundary problem. The numerical results are compared well with our experimental data. The influences of various parameters such as overpotential, proton conductivity, catalyst layer porosity, and catalyst surface area on the performance of catalyst layer are quantitatively studied. The model can be used to determine important catalyst layer design parameters for different working conditions. From the discussions in this paper, it is possible to design high performance, low cost cathode catalyst layer, and hence, to improve PEM fuel cell performances.