Abstract: Membrane electrode assembly（MEA）is the core component of proton exchange membrane fuel cells（PEMFC）. In order to study the influence of relative humidity on MEA,a two dimensional isothermal steady state model of the interdigitated flow field MEA is established. The PEMFC output performance,gas diffusion layer flow field,catalyst layer concentration field,ionomer properties and temperature distribution of MEA are analyzed under the same gas relative humidity of 30%,50%,70% and 90% at the inlet of anode and cathode. The results show that with the increase of relative humidity,the maximum output power density,the conductivity of ionomer and the temperature of MEA increase,but the molar concentration of hydrogen and oxygen in the catalytic layer decrease. The relative humidity increasing from 30% to 90%,the PEMFC maximum output power density increases by 1.7 times. Through numerical simulation,the physical and chemical changes in MEA can be revealed,which can provide the theoretical basis for optimizing the relative humidity of PEMFC inlet gas.