The existing publish/subscribe systems can’t match events with subscriptions based on the semantic of events, and they cannot support events with complex structure (such as graph structure). The Semantic Web technologies are introduced into the publish/subscribe system and an ontology-based publish/subscribe system is proposed. In this system, the concept model of events is represented as ontologies, the events are represented as RDF graphs, and the subscriptions are represented as graph patterns. The system can overcome the disadvantages of the existing publish/subscribe systems. Experimental results show that it has high matching efficiency.