Abstract: Aim To achieve intelligence,automation and effectiveness in the implementation of a missile fault diagnosis expert system,so as to improve the effectiveness in missile launching.Methods To study and develop fault diagnosis ES with AI technology.Results The prototype has more than 21 000 knowledge points,including more than 2000 rules.The longest item diagnosis time takes 0 67s,the shortest 0 13s.Thus,this system meets the required diagnosis time limit of 1 00s per item.Conclusion Application of expert systems in missile fault diagnosisis feasible and practical.