Closed circuit blade cooled gas turbines are drawing attention because of their efficiency compared with that of a conventional air cooled gas turbine. In a closed circuit blade cooled gas turbine, coolant is not discharged into the gas path, so dilution of the hot gas stream, rotor blade pumping loss and pressure loss due to mixing of coolant with the stream are drastically reduced. In this paper, two types of combined cycles, a closed circuit steam cooled gas turbine combined cycle CCSC, and a closed circuit air cooled gas turbine combined cycle CCAC are analyzed to verify the part load performance. The blade temperatures of both combined cycles are lower than at full load, that is, the blades are sufficiently cooled. Under 30% load in the CCSC, the coolant steam pressure is lower than the main gas stream because of a shortage of coolant steam.