Abstract: Under the conditions of sufficient N, P and K fertilization, growth index including aboveground biomass，dry root weight at different growing period and forage nutritional indexes, such as DM, CP, CF and CF at milky maturity stage of 8a Elymus sibiricus were measured in an artificial grassland on May in 2003 at well-bred site in Qinghai Province. The results showed that P and K fertilization increased the aboveground biomass of E. sibiricus by 16.25%50.32%, 5.86%35.74%, 10.72%44.37%, and 16.96%51.56%, 9.63%58.32%, 12.70%46.91% at heading date，flowering Period and milky maturity stage, respectively. At the rational level of NK or NP, the maximum aboveground biomass was observed when additional P 112.5 kg/ha or K 75 kg/ha was applied. Applying both P and K could increased the roots weight in 025 cm significant (P＜0.05). The root weight in depth of 05 cm and 025 cm of E. sibiricus was maximum when additionally applying P or K 75 kg/ha. The content of CP and CF increased first then decreased after application of P and K. Applying P 75 kg/ha or K 112.5 kg/ha resulted in the highest the content of CP and CF in the stem. The weight increased of biomass of aboveground and roots did not consistently positive correlation to the quantity of fertilizer application. The weight increasd with potassium fertilizer was higher than phosphorus fertilizer at the same fertilizer level.