As a result of the high demand for electricity in Iraq and the expected shortage in the supply of electric power due to the high temperatures in the summer, the existing gas turbine plants at Al Quds Gas Plant have been upgraded with an intake air cooling system. This is the main objective of this study for the model of the Quds gas station (frame 9E) with a capacity of 123 MW, the management of the proposed Brayton cycle was compared with the basic case without the cooling system and with an entry air cooling system (evaporative and fogging system). In this paper the performance enhancement of gas turbine power plants by cooling the compressor intake air with an evaporative cooler is studied. This study investigated the effect of inlet air cooling system on the performance of an existing gas turbine power plant in Iraq. The results show that for each 5oC decrease of inlet air temperature, net output power increases around 5-10% and the thermal efficiency increases around 2-5%. It is shown that the amount of this increase is higher when the pressure ratio is high and turbine inlet temperature is low. The results of this study shows that retrofitting of the existing gas turbine plant with inlet air cooling system gives a better system performance and may prove to be an attractive investment opportunity to the Iraq government and stakeholders of the plant.