Abstract: To promote the development of high-quality basic research, the National Natural Science Foundation of China (NSFC) has launched new reforms to optimize the layout of the discipline and its application codes. The discipline of atmospheric sciences in the Department of Earth Sciences of NSFC optimized the application code system and set up 15 application sub-codes since 2019 as its reform objectives. This article describes the background of the reforms, the logic structure, and the connotation for application code D0502 (Climate and Climate System), together with keywords for seven related research directions. Project application and funding of General Program, Young Scientists Fund and Fund for Less Developed Regions for application code D0502 during 2020–2021 are reviewed. This article aims to help researchers to learn about the development tendency of sub-discipline and to better understand the logical structure and connotation of D0502, providing a reference for a reasonable selection of research directions and corresponding keywords.