Abstract: Retrieval is an important way of information acquisition.The classic means of retrieval is still dwelling on logical similarity or difference between key words without consideration of the semantic relations.Based on knowledge organization system of ontology for the purpose of retrieval，a way of ontology-oriented document and query representation named semantic vector is proposed；further a way of similarity calculation is founded to create condition for semantic retrieval and to make the query result care more about semantic matching.At last an experimental study is presented under the guidance.