In order to better understand and explore the physiological and ecological response and adaptation of plants to environmental changes, Buddleja davidii distributed in the Balang Mountain in western Sichuan province was selected as the object. The contents of leaf non-structural carbohydrates (NSC), soluble sugar and starch, nitrogen concentration and nitrogen allocation fractions (fraction of leaf nitrogen allocated to photosynthetic apparatus P_P, cell wall P_CW and other components P_other) along an elevation gradient were compared to study their elevational patterns. Moreover, the correlations between the NSC, soluble sugar, starch and nitrogen allocations were analyzed. The results showed that the NSC, soluble sugar, starch and monosaccharides content of B. davidii leaves increased, while the soluble sugar/starch ratio did not change significantly along with elevation. These indicated that the accumulation of NSC at high elevation was determined by both soluble sugar content and starch content, while the increase in soluble sugar was mainly caused by monosaccharides content. Although leaf nitrogen concentration and P_P were not significantly different among elevations, P_CW and P_other decreased and increased along with elevation, respectively. Additionally, the NSC/N ratio of B. davidii leaves increased along with elevation, which was mainly caused by the increasing NSC content along the elevation rather than the insignificant nitrogen concentration among the different elevations. The contents of NSC and soluble sugar had significantly positive correlations with P_other, indicating that the accumulation of P_other and NSC content functioned together to improve the adaptability of the plants in the harsh environment at high elevation.