Among the auxiliary sciences of history field in the KDC 5th edition, several classification system problems are found with the fields of Archaeology, Diplomatics, Archival Science, Genealogy, and Biography. The purpose of this study is to propose their improvements. To achieve this purpose, first, this study compared and analyzed the Auxiliary Sciences of History field of LCC, DDC, KDC, NDC, UDC, CLC. Second, this study investigated the actual conditions of KDC in the library field to diagnose several application problems. Finally, based on the findings, the improvements of KDC were suggested.