Antropogenic activities have already generated and continue to increase the load of atmospheric nitrogen deposition on terrestrial ecosystems. The increase of nitrogen source reduces N-limition of tree growth, which can drive and enhance the carbon intake of forest. It means that the alternation of vegetation water use based on CO2 / H2O coupling would influence the regional water balance. So far, most studies on simulated atmospheric N depostion have mainly applied understory nitrogen addition. Such treatment ignores the fact that the nitrogen should be absorbed by the leaves and is, because of being directly added into the soil, soon incorporated into soil microbes, resulting in weakening the responses of trees to nitrogen. Additionally, nitrogen addition induces shift of carbon allocation that causes adaptive derivation of hydraulic architecture. It would indirectly affect the relation of stomatal conductance with environmental factors, which plays a crucial role in carbon intake and vapour exchange of forest. Accordingly, it is proposed that the adaptable change of hydraulic architecture drives the variation of stomata and indirectly affects the responses of tree water use to nitrogen deposition. We, for the first by means of simulated canopy N deposition in a deciduous broadleaf forest in Xin Yang, Henan Province, investigate the effects of nitrogen deposition on the whole-tree water use of dominant tree species and the related hydraulic driving. The results will contribute to revealing the interaction mechanism of forest C, N and H2O cycles and providing experimental supports for assessing and predicting the regional water balance in the future.