At present, inlet air cooling system of the heavy-duty gas turbine is lack of accurate economic evaluation model, so it can not provide accurate economic analysis. This paper put forward an economic evaluation model of spray evaporative cooler. Based on the meteorological data of practical engineering and engineering thermodynamics theory, the economic evaluation can determine the equipment parameters and economic indicators, guiding investment decision and equipment bidding through the calculation. Taking GE9171E gas turbine as an example, this paper analyzed the economy of the spray evaporative cooler. The results show that the output of each combined cycle unit will increase 7 751 026 kW?h each year, annual generating efficiency will increase 0.6%, and annual net income will be 996 100 yuan, if the spray evaporative cooler is applied for the gas tubine inlet air, which has obvious economic benefits and is suitable for hot and adequate water areas.