Abstract:The indices system of marine three-shaft gas turbine performance degradation is built,from the aspect of the overall engine performance, gas path components, the lubricating oil system, vibration,etc. The exhaust gas temperature margin, heat loss index, power deficit index , the extra heat ratio and thermal efficiency ratio are put forward , which are the characterization of overall engine performance degradation. The concept of degradation factor,characterizing the degradation of gas path components, is expounded. The degradation indexes of gas path components such as compressor, turbine and combustion chamber are put forward, including the adiabatic efficiency degradation factor, the flow capacity degradation factor, the surge margin,the thermocouple dispersion and so on. The solving and analysis methods of degradation indices are proposed , such as building mathematical model , statistical threshold method,small deviation method and Kalman Filter method,which are carried on the instance analysis. The paper constructs the basic framework for further research of gas turbine performance degradation.