Abstract: Knowledge of herbage nitrogen (N) and phosphorus (P) in plants is fundamental to the study of absorption and utilization of nutrients by the plants. In order to better understand limiting factors and plant adaption strategies to environmental factors in the grassland ecosystem, water and N enhancement experiments were carried out in a Stipa breviflora steppe. Four treatments were set up: nitrogen addition (ND), water addition (WD), nitrogen and water addition (NWD) and control (CK) with five replicates in a free grazed paddock in a S. breviflora desert steppe, Inner Mongolia. The S. breviflora leaf N and P concentrations and their stoichiometry under different treatments were analyzed. It was found that S. breviflora enhanced adaptability to barren habitats by increasing leaf N content. Uptake of N by S. breviflora was limited by low soil N and water contents. The absolute leaf N and P contents and the N:P ratio were more sensitive to the environmental addition of N and water in mid season than in late season. The availability of environmental N greatly influenced the leaf N and P contents and N:P ratio in mid season and the N:P ratio in late season when plants were withering. However, the availability of water only affected the leaf N and P content in mid season and not in late season.