Leaf delta C-13 is widely used to explain plant strategies related to resource availability in different environments. However, the coupled response of leaf delta C-13 to precipitation and temperature as well as the relationship between leaf delta C-13 and leaf traits remain unclear. The leaf delta C-13 and its relationship with leaf traits [leaf size (LS), leaf length (LL), leaf width (LW), leaf length to width ratio (L:W), specific leaf area (SLA) and mass-based leaf nitrogen concentration (N-mass)] were investigated on the dominant shrub species Nitraria tangutorum Bobr. in the arid region (Dengkou and Minqin) of northwestern China under the simulated increasing precipitation (PGS) and ambient temperature (TGS) in plant growing season from 2008 to 2010. Our results showed that LS, LW, LL, SLA and N-mass significantly increased with increasing PGS, but had decreasing tendencies with increasing TGS. However, the majority of the negative relationships between leaf traits and TGS were not obvious in Minqin. At the two study sites, L: W increased simultaneously with increasing PGS and TGS. There was a shift in the negative leaf delta C-13-PGS relationship across Minqin and Dengkou, which lead to the lacking effects of precipitation on leaf delta C-13 across the two sites, and higher leaf delta C-13 at lower precipitation in Minqin. Across Minqin and Dengkou, PGS could only explain 14% of the variation in leaf delta C-13. The combination of PGS and TGS could explain 64% of the variation in leaf delta C-13. Leaf traits (LW and L: W) further improved the estimation of leaf delta C-13. The combinations of PGS, TGS, LW and L: W could explain 84% of the variation in leaf delta C-13. Our study demonstrated the importance of leaf traits in exploring the responses of leaf delta C-13 to global changes in arid ecosystems.