With the development of agricultural research and production, agricultural information and data processing technology have become increasingly demanding. In recent years, organizing and expressing semantic knowledge based on the form of ontology has become the focus of research in artificial intelligence field. And the construction of ontology-based knowledge base is the basic condition. HNC theory has great advantages in processing of Chinese character. However, complexity of the system has restricted its development. This paper summarized the existing research results, took rice production (cultivation) and processing as an example, proposed an idea and methods for the knowledge base construction of agricultural ontology based on HNC theory.