A combined cycle power plant comprises a gas turbine system and a steam cycle system having a steam turbine to be driven by the steam generated by the waste heat of the exhaust gas of the gas turbine system, wherein the steam from the steam cycle system flows through a gas turbine cooling system of the gas turbine to cool the gas turbine blades and other elements of the gas turbine system to be cooled and the waste heat of the gas turbine system is effectively collected. The gas turbine cooling system has two or more than two cooling ducts formed in two or more than two elements of the gas turbine system to be cooled such as the gas turbine blades and the combustor of the gas turbine system so that steam is made to flow through the cooling ducts of these two or more than two elements to be cooled to effectively and maximally exploit the cooling potential and the waste heat collecting potential of the steam and hence improve the overall thermal efficiency of the plant.
