Abstract: Based on the theory of general Petri net, fault tree technique and theory of fuzzy set, a theory system of fuzzy Petri net suitable for fault diagnosis is established, which is used for an example of fault diagnosis for FMS. This method has the advantages of objectivity, strong expression ability,easy inference, etc. and it can exactly describe the properties of fault phenomenon and coherence of fault space.

Key words: malfunctions, diagnosis, faulttrees, models, stateestimation