In order to solve the problem of recall ratio and precision of the component query in the Semantic Web environment,the software component query algorithm based on ontology similarity is proposed.The paper first introduces the formal ontology definition and a component facet description method.The component ontology is formally described in the Web ontology language (OWL). Then,according to the concept of ontology similarity theory and the deficiency of the matching formula of component facet,the match degree of the matching formula of component facet is replaced by the concept similarity of component ontology;improvement and analysis are made in the matching formula of component facet.Thus,the ontology similarity query algorithm is put forward.By calculating the faceted ontological concept similarity of the component query tree and the trees corresponding to the various subcomponents,and then comparing the degree of similarity with the matching formula of component facet,the algorithm retrieves the highest degree of similarity of components.The result of the experiment indicates the algorithm has an ideal recall ratio and precision.