The invention relates to an online proton exchange membrane fuel cell fault diagnosis method based on low-frequency impedance and an electrochemical impedance spectrum. The method comprises the following steps of: 1) online comparing measured low-frequency impedance with a low-frequency impedance fault threshold, and 2) carrying out classification and fault diagnosis on the electrochemical impedance spectrum by using a fuzzy logic-based fault diagnosis algorithm. The method disclosed in the invention has the beneficial effect that the online proton exchange membrane fuel cell fault diagnosis method based on low-frequency impedance and electrochemical impedance spectrum measurement is provided. The low-frequency impedance is used for monitoring the state of the proton exchange membrane fuelcell, the fuzzy logic is used for classifying the state of the electrochemical impedance spectrum, online fault diagnosis based on the low-frequency impedance and the electrochemical impedance spectrum is achieved, and the actual application scene of the electrochemical impedance spectrum is greatly expanded.