In this study, a combined cycle power plant with a nominal capacity of 500 MW, including two gas units and one steam unit, was considered by the mathematical model of thermodynamic modeling and the results of the modeling were controlled by the design information of the system. Then, the objective functions are optimized by considering the decision variables. In this multi-objective optimization that has been carried out by Non-Dominated Sorting Genetic Algorithm (NSGA-II), three objective functions of exergy efficiency, CO₂ emission and produced power costs composing of the cost of injected fuel into combustion chamber ,cost of exergy destruction, investment cost and cost of environmental pollutants have been studied. The results indicate that the efficiency of combined cycle power plant depends on design parameters including gas turbine input temperature, compressor pressure ratio, and pinch point temperature and any change occurring in these parameters may lead to noticeable change in objective functions, so that the efficiency of this power plant is increased after optimization up to 8.12 % and heat rate is correspondingly reduced from 7233 (kJ/kWh) to 7023 (kJ/kWh). Similarly, exergy destruction in total system shows 7.23 reduction.