The mathematical simulation of gas-liquid two-phase flow of the proton exchange membrane (PEM) fuel cell under mechanical stress was studied. In this study, a two-dimensional, non-isothermal two-phase flow Multiphysics steady-state model of PEM fuel cells was established. The model comprehensively considered the solid mechanics, electrochemistry, heat and mass transfer and gas-liquid two-phase flow. The two-phase flow distribution of PEM fuel cells under mechanical stress was studied. The computational results showed that the stress of the porous medium under ribs was significantly greater than the stress under the flow channel. Stress concentration obviously occurred at the junction of the ribs and the flow channel. Liquid water was only condensed at the cathode and mainly formed in the porous medium under the ribs. As the current density increased, the cathode relative humidity gradually increased, however, the relative humidity of the anode decreased. Cathode liquid water saturation increased when current density increased.