In this paper, a non - isothermal and two-phase flow in the cathode gas diffusion layer (GDL) of PEM fuel cell is modeled. To achieve more accurate boundary conditions, other components of fuel cell (membrane and anode GDL) are modeled. Governing equations including energy, mass and momentum conservation and auxiliary equations are solved by numerical method and the effect of gas mixture pressure in channels, relative humidity and effect of contact and mass exchange between two phases are investigated. Results show, it is necessary that both the contact and mass exchange between the gas and liquid phase to be considered. The performance curve and temperature distribution for single and two phase flow are compared for different amount of cathode channel humidity. The relative value of performance and temperature for single and two phase flow depends on the humidity of cathode channel. With increasing the cathode pressure from 0.5 to 5atm the value of water content in membrane and gas diffusion interface will increase about 20%. With increasing the water content in the membrane therefore the ohmic loss is reduced. With the reduction in the ohmic loss the temperature distribution along the fuel cell decreases but if the anode pressure increases the temperature distribution along the fuel cell increases. Keywords