Fault detection and diagnosis methods for non—linear system based on wavelet neural networks are researched．Wavelet analysis and feed-forward neural networks are fused，and the algorithm is inferred．Method of wavelet neural networks is used in fault diagnosis for the lubricant system of the oA!roen-sine．Results of simulation and tests show that this method，which is good to fault diagnosis for non-linear systems，does better in convergence speed，and is not sensitive to the inputs of the network．