[Purpose/significance] A detailed comparison of the mapping between the Cooperative Patent Classification System (CPC) and the International Patent Classification System (IPC) is intended to provide references for the use of CPC and IPC for patent classification.[Method/process] This paper made a detailed mapping number analysis between CPC and IPC in terms of the class, subclass, group and subgroup on their common A-H sections. [Result/conclusion] The classification principle between the Cooperative Patent Classification System (CPC) and the International Patent Classification System (IPC) is basically consistent and CPC is more subdivided than the IPC. The “2000 series (indexing)” and the Y section of the new technology are added, showing CPC’s high extensibility. We believe that as a strong compatibility and high degree classification system, CPC will become an efficient tool to improve the efficiency of retrieval and optimize the review quality.