Using membership function and neural network (NN) develops a motor diagnosis system based on fuzzy neural network (FNN) in this paper. According to literature and experience principle, the relationship between fault and frequency spectrum is built up as the rule of fuzzy diagnosis and the training data of NN. In experiment, to use spectrum analyzer pick up the vibration signal of motor, then transform the signal into frequency domain by fast Fourier transforms and classify it by membership function, and detect this classified data in NN. In this paper, comparing with the detect result of FNN, fuzzy, and NN in two examples prove that FNN is better than other methods for multiple fault diagnosis.