This paper describes a theoretical model to investigate effects of different air parameters on the performance of PEM fuel cell. Parameters taken into considerations in the study are air mass flow rate, pressure, temperature and relative humidity. This study is applied on a fuel cell with a across section area of 218 cm² stacked in a series of combined 110 cells. The observed effects on the fuel cell performance are presented as system power, efficiency and polarization curves. The stacked cells may produce an overall power output more than 20 kW, this model studies the effects in two cases the first with constant relative humidity effect, and the second with different relative humidity effect. This model monitor the effects on PEMFC performance by using the V-I polarization curves. It showed that with the increase of air pressure, temperature and relative humidity the power increases nearly up to 8 %, in the other hand with the increase of air flow rate the performance is decreasing.