With the rapid development of Sematic Web, application of ontology spring up and ontology reasoner application are widely used. Ontology reasoner is used to reason and query semanteme, and is one key technology in implementing Sematic Web. This paper introduces the techniques, classification, and structure of Ontology reasoner, and then introduces several Ontology reasoners. Lastly, this paper summarizes the application and the future work to be done on this topic.