Abstract: As the climatic transitional zone of warm temperate and subtropical in China, Qinling-Daba Mountains has been one of the hotspots of biodiversity research in China. The climate showed a great impact on the spatial distribution of plant diversity in Qinling-Daba Mountains. Based on the seed plant species database of Qinling-Daba Mountains and its adjacent areas, firstly, this paper analyzed the spatial distribution pattern of order, family, genus, species diversity, tree, shrub, herb diversity, and diversity of species endemic to China, and described the spatial distribution characteristics of plant diversity in the transitional zone of Qinling-Daba Mountains. Secondly, combined with the temperature and precipitation data of Qinling-Daba Mountains, we revealed their synergistic variation characteristics in spatial distribution by carrying out the spatial overlay analysis of plant diversity and environmental indicators. Thirdly, plant orders, families, genera, species, arbors, shrubs, herbs, and endemic species of China were clustered, and the clustering results were shown spatially, thus clearly showing the spatial clustering law of plants in Qinling-Daba Mountains. Finally, we summarized the climatic characteristics of the mutation location of plant diversity and determined the plant indicators for the division of subtropical and warm temperate zones. The results showed that the diversity of orders, families, genera, and species, and the diversity of trees and shrubs had a spatial distribution pattern gradually decreasing from south to north. The diversity of plant families and genera had a clear boundary, and the species diversity had an obvious transitional zone. The dividing line of more in the south and less in the north was roughly located in Funiu Mountains in the eastern (Nanzhao County, Neixiang County, Shangnan county and Xunxi county) - south of Taibai Mountains in the middle (Zhen'an County, Shiquan County, and Yang county) - Mian County, Wudu District, Wen County and Pingwu County in the western, that was, the south flank of Qinling Mountains. The transitional zone with more in the south and less in the north covers the wide area between the south slope of Funiu Mountains and the north slope of Shennongjia in the eastern. The relatively narrow area between the south slope of Taibai Mountains and the north slope of Micang Mountains in the middle was almost a line in the west, which almost coincides with the boundary. In terms of the diversity of endemic species in China, the internal Qinling-Daba Mountains were higher than the external, which further confirmed the strong transition in Qinling-Daba Mountains. The results can provide scientific evidence for the protection of plant diversity in Qinling-Daba Mountains, and help human beings understand the impact of the ecological environment on the forest ecosystem.