To solve the problem that the model of multi performance parameters cannot express the engine degradation at different thrusts,the extreme shock model was used to describe the thermal shock effect of full-power takeoff on the hot-end components by using a single performance parameter for civil turbofan engines,and a linear degradation model was used to describe the normal deterioration process,the performance reliability degradation model of an engine was set up.With the engine V2500 full-life exhaust gas temperature margin (EGTM) data,the maximum likelihood estimation was used to create the engine specific performance reliability expression and its parameters were estimated as well.The incomplete EGTM data of this engine in the same fleet was used to verify the model and the engine on-wing time was estimated.The result shows that the error between the predicted on-wing time and actual on-wing time is less than 3%,so the model is effective.