Abstract: According to the complicated corresponding relationships between fault symptoms and fault reasons when giant asynchronous motor occurring fault, a new fault diagnosis method of motor using neural network expert system was presented. The expert system works as the shell of neural network, making full use of characteristics of expert system and neural network individual. The paper introduced the composition, function, algorithm and its realization of the system. The algorithm also emulated neural network toolbox with MATLAB. The results showed that the algorithm is feasible and the diagnosis accuracy is improved.