Due to the complex structure of nuclear facilities in a high irradiation environment, people were hard to approach it, In view of these situation a fault diagnosis method based on HMM(Hidden Markov Model) of capturing the audio signal while facilities were operating was proposed. With the strong modeling ability, HMM could be applied to analyzing such as audio signal non-stationary time signal. By using this method, the original mechanical structures of nuclear facilities were not destroyed. The preposed sensors were needed as few as possible by the whole diagnosis system and which had a simpl...