Abstract: In the field of digital humanities, time ontology is one of the key applications when we are building a knowledge base of ancient books in depth through the semantic web technology. In view of the fact that the ancient Chinese timing methods are complicated and changeable, this article takes “refinement” as the main idea, systematically lists the ancient Chinese time pedigree from coarse to fine in the time dimension, and combines the two perspectives of historical context and cognitive context to build the “ancient Chinese time ontology” (ACTO). ACTO covers five major modules of time system, time representation, time reference frame, annotation and transformation. Through case demonstration, technology realization and application exploration, it explores ACTO’s application framework and scene in the field of digital humanities, which is typified by the ancient books database.