Climate warming promotes alpine plant migration to higher elevations, yet how they adapt via stoichiometric homeostasis remains unclear. We measured plant C, N, and P traits and homeostasis across community and functional group levels in three alpine vegetation types—meadow (3200–3400 m), shrubland (3400–3700 m), and cushion vegetation (3700–4400 m)—along an altitudinal gradient in the northern Qilian Mountains, Tibetan Plateau. Shrubland, as ecotones, had higher soil C and N, with plant communities showing the highest N and N:P but lowest C:N. At the functional group level, Poaceae (Gramineae) and forbs had the highest N and N:P, while Cyperaceae had the highest P in shrubland. Notably, Cyperaceae in shrubland exhibited weak P and C:P homeostasis. Poaceae (Gramineae) were mainly influenced by soil, Cyperaceae by climate, and forbs by elevation. Structural equation modeling showed elevation indirectly affected stoichiometry via climate and soil; climate influenced nutrient contents, while soil controlled C:N:P ratios. These results reveal diverse nutrient regulation and survival strategies in alpine plants, enhancing understanding of adaptation and community assembly under climate change.