[Objective] The nutrient content and ecological stoichiometric characteristics of plants across various altitudinal gradients in fragile forest ecosystems in arid regions were analysed in order to provide scientific support for their nutrient management. [Methods] This study focused on the dominant plant species at five distinct altitudinal intervals, i.e. 1 730, 1 799, 2 025, 2 487, and 2 544 m in the Helan Mountains National Nature Reserve. The variations and correlations of carbon (C), nitrogen (N), and phosphorus (P) contents and stoichiometric features in leaves, fine roots, and soil along these gradients were analysed. [Results] ① Soil organic carbon (SOC) displayed a unimodal pattern with altitude, peaking at 2 487 m (42.92 g/kg). Soil total nitrogen (TN) levels at the three highest altitude sites (2 025, 2 487, 2 544 m) were significantly greater than those at the two lowest altitudes (1 730, 1 799 m), whereas total phosphorus (TP) remained relatively stable. The C∶P and N∶P initially increased and then decreased with increasing altitude. ② There was no significant change in leaf and fine root C across altitudes, but the P content increased with altitude. Fine root N content progressively declined with altitude, whereas leaf N exhibited a fluctuating trend. At high altitudes, the N∶P ratio in the leaves and fine roots was less than 14; however, at low altitudes, the ratio exceeded 16. ③ Nutrient concentrations in the leaves were significantly higher than those in the fine roots. ④ Correlation analyses revealed that C content in leaf positively correlated with SOC, TN, C∶P and N∶P in soil. In contrast, N content in leaf and fine root significantly decreased as SOC, TN, C∶P and N∶P in soil increased, and the relationship between leaf and fine root P and soil TP was not significant. [Conclusion] Plant growth at high and low altitudes is mainly limited by N and P, respectively. Leaves of dominant plant species at different altitudes exhibit higher nutrient contents than their fine roots, and variations in soil nutrient supply due to altitude influence the N, P and stoichiometric characteristics of plants in the Helan Mountains.