Abstract: The east-west extending Kunlun-Qinling tectonic system in central China has a major environmental effect of dividing China into northern and southern parts, but there is still controversy over the location of the north-south dividing line and the boundary of the north-south transitional zone in China. Therefore, this paper presented an in-depth analysis of the geographic structure and extent of the Qinling-Daba Mountains and the Huaihe-Yangzte Plains to determine the scope and properties of the north-south transition zone in China. The study showed that the north-south transition zone in China consisted of the Qinling-Daba Mountains in the west and the Huaihe-Yangzte Plains in the east, and was typically characterized by zonal evergreen and deciduous broad-leaved mixed forests, corresponding to the coldest monthly average temperature of 0 ℃~4 ℃ and extreme minimum temperature of −10 ℃~−20 ℃. The appearance of evergreen broadleaved trees in the lower parts of the southern flank of the Qinling Mts. did not mean the starting of a subtropical zone, but the starting of the so-called "north-south transitional zone" in a narrow sense. The Huaihe-Yangtze Plain had obvious characteristics of high summer temperatures and low winter temperatures, and winter climate indicators were more controlling than summer temperature indicators. The existence of the Qinling-Daba Mountains and relatively very low winter temperature were responsible for the formation of the north-south transitional zone of China, thus developing a large transitional area of about 700 000 km² with an east-west length of 1 750 km and an average width of 400 km. Compared with such terms as north-south dividing line or boundary belt, the concept of the north-south transitional zone can reflect the physio-geographic feature of the Qinling-Daba Mountains and the Huaihe-Yangzte Plains, can embody the uniqueness of the physio-geographic pattern of China, and can more significantly promote the understanding of China's geographical structure and function.