In 2010, measurements were conducted on the foliar delta13C, photosynthesis, CO2 diffusive conductivity, nitrogen content, photosynthetic nitrogen use efficiency (PNUE), and special leaf area (SLA) of Salix atopantha at different altitudes (2350 m, 2700 m, 3150 m, and 3530 m) in Wolong Natural Reserve. With the increase of altitude, the foliar nitrogen content (especially the nitrogen content per unit leaf area, N(area)) and the PNUE increased, and the foliar delta13C had a significant increase, with an increment of 1.4 per thousand per 1000 m altitude. The stomatal and mesophyll CO2 diffusion conductance also increased with increasing altitude, which had definite negative effect on the increase of foliar delta13C, but the effect was not strong enough. Comparing with CO2 diffusion conductance, carboxylation capacity was a more important factor limiting the P(c)/P(a), and even, the foliar delta13C. At altitude 2350-2700 m, air temperature was the main factor affecting the allocation of nitrogen in S. atopantha photosynthetic system, whereas at altitude 2700-3530 m, light could be the main affecting factor. No significant difference was observed in the SLA at different altitudes.