The alpine steppe on the Qinghai-Tibetan Plateau (QTP) has been experienced a long-term influence by grazing livestock, resulting the changes in the material cycle of grasslands. By investigating the responses of plant community composition and soil nutrient to grazing regimes (i.e., continuous grazing and rotational grazing) and intensity (4, 6, and 8 sheep per hectare), we examined the mechanisms of maintaining the productivity, tried to answer the questions how grazing regulate the aboveground net primary productivity (ANPP) of the alpine steppe the QTP. Our results showed that medium rotational grazing increased the soil stoichiometry including TC: TN ratio, TN: TP ratio, and TC: TP ratio, whereas continuous grazing only increased TC: TP ratio. Structural equation modeling further revealed that grazing affected soil available nutrient by intermediating soil nutrient balance, and increased NH4+-N and NO3--N. Compared with continuous grazing, rotational grazing could significantly improve ANPP. Soil available nutrients respond preferentially to grazing compare with plant diversity to maintain grassland productivity in the alpine steppe on QTP. These results are meaningful for developing the rational grazing management practices on grasslands.