Effective knowledge modeling is one of the key issues in Cognitive Radio(CR). This paper proposes an ontology-based model for CR knowledge representation. Concept extraction and class analysis is performed for CR knowledge described by natural language，and web ontology language is adopted to implement the ontology of CR knowledge. Then reasoning is conducted with the ontology. The experiment result shows that the proposed method supports knowledge sharing and reuse，can integrate heterogeneous radio knowledge，and enables CR to understand their own state and external environment，which provides the basis for CR reconfiguration in decision-making.