The geographical pattern of plant functional traits and its environmental drivers is a central question in plant population ecology. Leaf functional traits can directly affect the physiological and biochemical processes of plants, reflecting the resource acquisition strategies and adaptation mechanisms of plants. In this paper, with the national key protected plant Davidia involucrata as target species, we measured 17 functional traits of 18 populations across its natural distribution range in China, and analyzed the effects of environmental factors on leaf functional traits. At local scale, the coefficient of variation of leaf traits functional ranged from 1.48% to 24.81%. The variation degree of leaf carbon phosphorus ratio was the largest and the variation degree of leaf organic carbon content was the smallest. With the increase of longitude and latitude, the leaf area, leaf thickness and leaf serration number of D. involucrata decreased significantly. With the increase of altitude, the leaf thickness, leaf dry matter content, leaf area and leaf phosphorus content of D. involucrata increased significantly, and the leaf shape became wider and more round. Leaf serration enhanced the adaptability of D. involucrata leaves to cold. Significant leaf trait–geography correlations were mediated by climatic and/or soil factors. Environmental factors explained 79.90% of the variation of D. involucrata leaf traits. The variation of leaf traits was mainly driven by geographical variables and climatic factors, and was also affected by soil factors. Among the climatic factors, annual precipitation is the strongest explanatory factor for leaf trait variation, and annual precipitation can explain leaf trait variation more than annual average temperature. In general, the functional traits of D. involucrata leaves showed a clear geographical pattern at the species distribution scale, in which precipitation and soil nitrogen content played an important role in the formation of geographical pattern.