In this paper, a new kind of automated fault diagnosis algorithm is proposed. It is a new data-mining algorithm with ontology-based. This algorithm doesn?t only find low-level rules which usually not interesting, but also can find high-level rules which described by high-level concepts. In this paper, we use ontologies provide a mechanism, in data mining, by which domain specific knowledge may be included to aid the discovery process and can find multi- level classification rules, the rules are described by high-level concepts. So it can provide more interesting rules for enterprise. Finally, a study case is given to explain the practical application with the fault diagnosis bases on ontology, and is given encouraging results.