Abstract: The algorithm described in the paper is one of the important instruments for the establishment of aero engine expectant cycle to supervise aero engine scientifically and effectively.By means of experimental method of using real specimens,the optinal algorithm which can estimate aero engine expectant cycle quickly and precisely among BP neural network,GA (genetic algorithm) and compound GA BP can be found.It shows that GA BP algorithm can simulate expectant cycle excellently.First it searches weights of neural network grossly using genetic algorithm,then is trained by using BP network.It has been proved to be effective by real instances.Two softwares have been made.