A catalogue organized according to the subject system of literature and the literature classification adopted by the library. Its main functions are as follows: ① it can systematically reveal the documents collected by the library according to knowledge categories; (2) Reveal the relationship between a certain knowledge category and other knowledge categories, and provide the retrieval way of related subject literature. Classified catalogue is one of the main categories of library catalogue, but it can only be used if you are familiar with the classification system.