Abstract: A framwork of virtual maintenance knowledge management system of power generation equipment based on ontology was presented in this paper. According to the content of maintenance document package and the characteristics of equipment information source knowledge in the field of virtual maintenance of steam turbine in power plant,the maintenance knowledge was sorted,and the contents of maintenance document package were reasonably classified and modularized.The ontology models of event process ontology,state ontology,cause ontology,maintenance entity ontology and maintenance decision ontology were established respectively,which can reasonably classify the maintenance contents.The proposed virtual overhaul method provides good semantic retrieval and knowledge expression functions for virtual maintenance of equipment,which improves the efficiency of enterprise maintenance.