OWL DL, being established by W3C, is a Knowledge Representation Markup Language for the Semantic Web. OWL DL is a new synthesis of research on KRML for the Semantic Web, which needs to be expressive enough for representing knowledge and computationally tractable for inference of large-scale applications. In the domain of KR, description logic is researched as a trade-off between expressivity of knowledge and complexity of reasoning problems. In this paper, description logic is used as the formal foundation of OWL DL, the corresponding relation between OWL DL and Description Logic is analyzed, every element of OWL DL is interpreted with the semantics of description logic; It shows that OWL DL is description logic's syntactic variant. So the research conclusions of description logic can be applied to OWL DL, and the foundation of investigating KR and reasoning problems for OWL DL is established. KEYWORDS OWL DL, Semantic Web, ontology, Description Logic