Phosphorus (P) addition has the potential to enhance grassland productivity under intensive grazing conditions. However, P addition regulates the balance between soil availability and plant uptake remain unclear. The aim of this study is to evaluate balance between plant and soil under supplement. Field experiment combining UG (no grazing and P addition), P0, P15 and P30 (grazing with phosphorus supplementation) in Mongolian grassland. Grazing at levels of 6 sheep/ha. We determined soil and plant of Stipa krylovii under four treatments, and Leymus chinenisis in UG. P supplementation increased both AGB and BGB of S. krylovii and increased PO₄³⁻ in soil at P30. Increasement of PO₄³⁻ in soil is considered to improve provide of phosphate for plant. As results, plants increased availability of phosphorus in the soil, and it might get the opportunity to grow even with little rain. On the other hands, it was considered that unexpendable phosphate may remained in the soil. AGB/BGB ratio between L. chinensis and S. krylovii was different. In addition, PO₄³⁻ in the soil may be related to the AGB/BGB ratio. This indicates that different species respond differently to phosphate, suggesting that changes in the balance of phosphate may affect species dominance.