Fuel cell technology is recently becoming one of the most interesting fields for the car companies to invest in. This interest is because of their high efficiency and zero environmental pollution. Polymer electrolyte membrane fuel cells (PEMFC) are the most appropriate type of fuel cells for use in vehicles due to their low performance temperature and high power density.Air and fuel mass flow rate and partial pressure, fuel cell stack temperature, relative humidity of fuel cell membrane and heat and water management are the effective parameters of fuel cell power systems.Good transient behavior is one of the important factors that affect the success of fuel cell vehicles. In order to avoid stack voltage drop during transient condition, the control system of fuel cell vehicle is required to preserve optimal temperature, membrane hydration and partial pressure of reactants across the membrane. In this paper, we developed a dynamic model for fuel cell power system. The compressor dynamic, supply and return manifold filling dynamics (anode and cathode), membrane hydration and time-evolving reactant partial pressure are the most significant parameters in transient and steady state of system. The effects of membrane humidity, varying inlet air pressure, and compressor performance condition on the generated power is studied in this paper.