The performance of Polymer Electrolyte Membrane (PEM) fuel cell is greatly affected by operating parameter so it is essential to evaluate the optimum value of operating parameter to maintain the stable performance. In this Work 3D multiphase model is developed in Gambit and then the geometry is solved in the commercial CFD software Fluent to predict the effect of relative humidity and stoichiometric ratio of air on the performance of polymer Electrolyte Membrane fuel cell. The simulation results are presented in the form of polarization curves, which shows the effect of Relative Humidity and stoichiometric Ratio of air on the performance of the fuel cell. Result showed that the best performance obtain at 20% relative humidity of air when hydrogen is fully humidify and performance of PEM fuel cell increase by increasing the stoichiometric ratio of air when hydrogen and oxygen are both fully humidified but at high stoichiometric ratio increase in performance is negligible. The objective of this study is to explore the research in the field of PEM fuel cell.