In advanced combined-cycle power plants, significant improvements in the thermodynamic performance are mainly achieved by the development of more efficient gas-turbine systems. This paper evaluates the effect of selected decision variables in the steam system for optimization of Thermal Combined Cycle Gas Turbine (TCCGT) power plant using an iterative exergoeconomic. The design variables were the thermodynamic parameters that establish the configuration both of the steam and gas systems. The design data of an existing plant (Damavand power plant in Tehran-Iran) is used. Two different objective functions are proposed: one minimizes the total cost of production per unit of output, and the other maximizes the total exergetic efficiency. The analysis shows that the total cost of production per unit of output is 2% lower and exergy efficiency is 4% higher with respect to the base case. It demonstrates that selected decision variables have suitable results for the exergy analysis and cost effectiveness. Since, environmental pollution and energy shortage are the two factors limiting the development of the society; nevertheless, this analysis tends to optimally find the design parameters which result in a decrease in the fuel mass flow rate. Also, this reduction (about 5%) in the mass flow rate and increasing exergetic efficiency can decrease the environmental impacts.