In this study, the effects of the working pressure and temperature on the performance of the PEM fuel cell were investigated numerically. Non-isothermal, steady-state and single-phase model was used to examine the behaviour of the proton exchange membrane (PEM) fuel cells in the three-dimensional condition. The three-dimensional single-cell model has been developed within FLUENT 6.3 software by utilizing the PEMFC module. The results of polarization (voltage) variation curves and current density distribution were given and compared with each other. According to the results obtained, by keeping humidification and cell temperatures in equilibrium, the performance of the cell improves with the increasing cell temperature. In addition, the current density of the cell increases with the increasing operating pressure.