As an important cultural heritage, ancient Chinese stone arch bridges have profound historical, artistic and technological values. However, affected by multiple factors such as natural disasters and human activities, their historical features are gradually disappearing. Virtual restoration has become a key means to reconstruct their original appearance. However, how to obtain information such as the geometric appearance and texture of ancient bridges at different historical points requires the integration of knowledge in many aspects such as structural form, material technology, historical documents, and archaeological surveys. Therefore, in the face of this interdisciplinary problem, it is urgent to integrate and accurately express relevant knowledge. This paper proposes a knowledge expression method for virtual restoration of ancient stone arch bridges based on CIDOC CRM, which integrates top-down and bottom-up construction strategies, constructs an ontology model from the two dimensions of entity and process, and constructs a knowledge graph based on the Neo4j graph database to achieve semantic integration and visual association of interdisciplinary knowledge. Taking the Wanning Bridge in Beijing as an example, the verification results show that this method can systematically organize complex knowledge such as structural characteristics, historical changes and restoration activities, effectively improve knowledge retrieval efficiency, and provide semantic support for restoration decisions. This study not only provides technical support for the digital protection of ancient bridges, but also contributes new ideas to the knowledge modeling method of cultural heritage.