In this study, the first law analysis of the thermodynamics was applied using the data of a real gas-fired combined cycle power plant. The net power outputs of the system are calculated for the Brayton cycle and Rankine cycle as 48 MW and 12 MW respectively and the effect of changing environmental conditions on the system was examined. It is calculated that the gas turbine has an average efficiency of 38% and the combined cycle has 48% efficiency. With an increase in ambient temperature of 45 degrees C, the system has 22% reduction in net power, while the power required for compression in the compressor section has also increased. As the ambient temperature increased, there was a 20% reduction in specific fuel consumption in the direction of the decrease in air flow entering to the compressor. It has also been revealed that, the environmental temperature has a direct effect on the combined cycle power plant.