Since the Qinling-Huaihe line was delimited as the boundary between north and south China in 1958, discussions on the local position of the line, criteria for dividing temperature zones, the line's environmental effect, among others, are ongoing. The National Basic Resources Investigation Program "Integrated Scientific Investigation of the North-South Transitional Zone" launched in 2017, introduced the concept of north-south transitional zone (Qinling-Daba Mountains) and planned to explore the north-south dividing line from the perspective of transitional zone, so as to strengthen and make some breakthroughs in the study of the north-south division. The Qinling-Daba Mountains are the main body of China's north-south transitional zone, with multidimensional zonal structures and high degree of environmental complexity, biological diversity, and climatic sensitivity. The following 10 scientific issues need to be dealt with in the years to come: 1) The relationship between the north-south dividing line and the north-south transitional zone; 2) improvement of criteria for identifying subtropical and warm-temperate zones; 3) integral north-south series and variation of vegetation and soil types; 4) relationship between global warming and spatial change of key bioclimatic criteria; 5) decomposition and integration of multi-dimensional zonal structures in the Qinling-Daba Mountains; 6) pattern and mechanism of biological diversity and endemics; 7) the corridor effect of the Qinling-Daba Mountains; 8) regional environmental effect of the Qinling-Daba Mountains and implications for the national ecological security; 9) significance and position of the Qinling-Daba Mountains for the history and development of China; and 10) significance of the geographic structure of Western Qinling Mountains for the origin of the Chinese civilization. These key issues are not only the results of previous research, but also the starting point for further exploration and study in the future. They are intended to inspire and encourage an in-depth study of China's north-south dividing line or transitional zone, and to provide new perspectives and framework for the exploration of physio-geographic theories, biodiversity, and ecological security, and even the birthplace of the earliest Chinese civilization.