© 2015, Springer International Publishing Switzerland. Background and Aims: Plant growth and ecosystem processes in semiarid regions are limited by soil nutrient and water availability. Nitrogen (N) and phosphorus (P) status and the N:P ratio alterations among plant organs are critical in understanding the physiology and productivity of the grass-legume mixture system. This study aimed to identify the N and P distribution patterns and N:P stoichiometry of a local grass species mixed with a legume species under varying water and fertilizer supplies. Methods: A C4 perennial herbaceous grass Bothriochloa ischaemum and a C3 perennial leguminous subshrub Lespedeza davurica were grown in a pot experiment with a randomized complete block design consisting of four fertilizations (non-NP, +N, +P and +NP fertilizers), three soil water regimes (80, 60 and 40 % of soil water field capacity, FC) and six planting ratios (2:10, 4:8, 6:6, 8:4, 10:2, and 12:0, grass:legume plants, respectively). Plants were assessed for biomass production, N and P concentration and N:P ratios in various organs 202 days after sowing (DAS). Results: For the grass species (B. ischaemum), N and P concentrations of leaf, stem and root were higher when mixed with the legume (L. davurica) compared to its monoculture, and with a trend to decrease as its mixture proportion increased. Supply with P fertilizer (+P) increased N and P concentrations of B. ischaemum regardless of mixture proportions and soil water regimes. In mixtures, N concentration was the highest in the root system followed by the leaf, and the least in the stem. There was no significant difference in N:P ratio of the stem and the root across the mixture proportions under +P and +NP treatments, and among all soil water regimes, either. Root N:P ratio was significantly lower under +P and +NP than that under non-NP or +N treatment regardless of mixture proportions and soil water regimes. Conclusions: N and P capture and absorption in B. ischaemum were greatly improved when mixed with the legume species, L. davurica. The N and P concentrations in different organs were influenced by both fertilization and the mixture proportions. Application with combined N and P fertilizers enhanced N and P uptake in B. ischaemum. P fertilization should be considered when establishing artificial grassland using native species in the region.