A power plant system using a combined cycle is disclosed. The power plant system using a combined cycle according to the present invention includes: a gas turbine part which operates a gas turbine to generate power using a hydrocarbon based fuel supplied to the gas turbine part; an exhaust heat recovery power generation part for operating a steam turbine to generate power using steam produced by using air discharged from the gas turbine part as a heat source; and an evaporative make-up water supply part for supplying make-up water which is made by evaporating seawater using turbine filling steam discharged from the exhaust heat recovery power generation part as a heat source to the exhaust heat recovery power generation part. [Reference numerals] (AA) Air/Fuel; (BB) Exhaust; (CC) Turbine to be enclosed increase(Gland seal steam); (DD) Supplement water; (EE) Seawater; (FF) High concentrated salt water(Brine); (GG) Raw water(Seawater)
