In the present study, a CFD (computational fluid dynamics) three-dimensional model is performed to investigate the effects of the inlet temperature on the power density, pressure and local transport phenomena of a single cell PEMFC (proton exchange membrane fuel cell) with straight channels. Deferent inlet temperatures of the reactants (333, 343 and 353 K) have been investigated using ANSYS-FLUENT. The interest of our work is focused on obtaining I-P and I-V curves as well as the pressure, hydrogen, oxygen and water mass fraction profiles to analyze the effect of the oxygen and hydrogen inlet temperature on the current, voltage and power densities of the studied PEMFC. From the results obtained its appears that the variation in the inlet temperature values of the PEMFC has a significant influence on the cell performances at medium and higher current density. Therefore, the results analysis of the three-dimensional and single-phase model indicates that the increase in the reactants’ inlet temperature of the studied PEMFC shows a negative impact on the generated power densities, which have an inversely proportional effect.