Abstract: This paper studied the civil aviation aircraft engine.The reliability of the engine has been studied by the performance degradation theory and stochastic process methods.Firstly,the reliability model based on Brownian motion with drift was built by analyzing the performance degradation process of the engine.Then,the degradation-time prediction method for current degradation signals was developed by using the characteristic of Brownian motion.These models were applied to practical situations.It is shown that the proposed methods are feasible and the prediction accuracy meets the needs of the project.Also,it provides a foundation for scientific management of engine fleet of airlines.