[Objective]To study the effects of warming on nitrogen cycle and water use efficiency by isotopic method, and to explore the response of the water use efficiency and the nitrogen saturation state of subtropical Cunninghamia lanceolata juveniles grown in subtropical region to global warming. [Method]The experimental site is located in the Global Change Experimental Platforms,in Sanming of Fujian Province,China. The heating cables were used to artificially induce the warming. The treatments of control ( CT) and warming ( W) were set up. The leaves of C. lanceolata and surface soil ( 0 10 cm depth) were sampled to examine the contents of their stable N and carbon ( C) isotopes,i. e.,delta~(15)N and delta~(13)C,and the contents of C and N. [Result]Compared to the control treatment ( - 2.79),the foliar delta~(15)N of the warming treatment ( 0.40) significantly increased by 3.19; but no significant difference was found in the leaf N contents between the control and the warming treatments. After warming, there was a significant increase in surface soil delta~(15)N,and leaf 15N enrichment index was closer to 0 compared to that in the control treatment. The foliar delta~(13)C of the warming and control treatments were - 29.35 and - 29.08,respectively. There was a significant positive correlation between foliar delta~(15)N and delta~(13)C. [Conclusion]These findings suggest that the temperature is an important factor affecting N cycling in subtropical regions. Warming can increase leaf and soil delta~(15)N significantly,and the metabolism of carbon and nitrogen complement each other.