Abstract: Gas turbines often suffer compressor fouling, turbine corrosion and erosion during the operation, which lead to performance degradation of components and brings negative effect on the operating state of the engine. In this paper, the variations of the surge margin of high-pressure compressor, maximum allowable output power and thermal cycle efficiency were investigated based on the performance simulation model during the isentropic efficiency attenuation and flow capacity variation of high-pressure compressor, high-pressure turbine and power turbine of LM2500+SAC gas turbine used in gas pipelines. It is indicated that isentropic efficiency attenuation of high-pressure compressor and high-pressure turbine can lead to the significant reduction of the maximum allowable output power of gas turbine and correspondingly the thermal cycle efficiency decreases as well, but the change of the flow capacity of both components has less influence on the performance of the overall unit. Equipping a dual-rotor aeronautical modified gas turbine with power turbine which has adjustable vanes, the maximum allowable output power of the engine under sub-health state can be improved effectively by increasing its flow capacity and fuel supply. The research results provide the reference for the location of faulty components and the optimization of gas turbine operation.