Abstract: To quantitatively diagnose the gas turbine performance degradation trend caused by compressor blade fouling during actual operation, a gas turbine performance degradation prediction method was proposed based on multiple nonlinear regression model. Taking the PG9351FA gas turbine as an example, performance degradation models were set up respectively for the compressor inlet air flow, compressor pressure ratio, isentropic compression efficiency and gas turbine power after offline water washing of the compressor. Results show that, the decreasing rate of gas turbine power caused by compressor blade fouling is approximately 1.7 times that of the compressor inlet air flow. Running for 2 000 hours after offline water washing under baseload condition, the compressor inlet air flow would be decreased by 3.26%, while the pressure ratio and isentropic compression efficiency be reduced by 3.04% and 2.62% respectively, leading to a comprehensive reduction of gas turbine power by 5.54%. With further rise of operation hours, the performance degradation rate gets stable.