This study describes the theoretical and experimental analysis of an MW-level three-shaft gas turbine. A thermodynamic-cycle calculation method of a three-shaft gas turbine with a hybrid cooling model is developed. Certain test data from the real engine, such as power output, fuel flow rate, overall efficiency, power turbine inlet and outlet temperatures, rotational speeds of the gas generator high-pressure shaft and low-pressure shaft and air flow rate, are obtained via experimental research. The empirical parameters in the proposed calculation method and the cooling model are revised via comparison between the calculated results and the test data. The effectiveness of the thermodynamic cycle performance analysis method of the three-shaft gas turbine and the cooling model is also verified. Based on the calculation method, further investigation of the characteristics of the gas turbine is performed on a wide load range when the power turbine operates at a fixed physical speed. The results show that a variable-angle nozzle significantly affects the performance of the gas turbine. The surge margin of the low-pressure compressor is also shown to be particularly important when the gas turbine operates at a high gas temperature with a more open variable-angle nozzle; also, due to the limitations imposed by the temperature control line, the high-pressure compressor always have an adequate surge margin. Throughout the operation range, the low-pressure and high-pressure turbines have high isentropic efficiencies; however, opening or closing the nozzle would decrease the isentropic efficiency of the power turbine compared with the ideal design condition. When the power output is constant, closing the nozzle causes the turbine inlet temperature to increase, thus increasing the efficiency of the gas turbine. Therefore, the optimal operating line under a wide range of loads is obtained by combining the adjustment of the variable-angle nozzle and the gas temperature. (C) 2016 Elsevier Ltd. All rights reserved.