Test case is one of the most important part of software testing. Reusing available test cases is an effective means to reduce the cost and improve the efficiency of software testing. In order to efficiently reuse test cases, a unified and standard format to describe test cases is needed. Therefore, this paper presents a reusing method based on ontology. The test case ontology is created by Protégé Ontology Editor and described by OWL (Web Ontology Language). At last, an example to illustrate the application of this method is to be discussed.