This paper improves the traditional text mining technology which cannot understand the text semantics. The author discusses the text mining methods based on ontology and puts forward text mining model based on domain ontology. Ontology structure is built firstly and the “concept-concept” similarity matrix is introduced, then a conception vector space model based on domain ontology is used to take the place of traditional vector space model to represent the documents in order to realize text mining. Finally, the author does a case and draws some conclusions.