Root is one of the most important carbon pools in grassland ecosystem. Analyzing the biomass of plant community, the carbon distribution characteristics of roots with different diameters, and the response of root growth characteristics to changing precipitation contributes to understand the carbon and nitrogen cycle and process of roots and soil in an alpine meadow under global change. In this study, we investigated the biomass of plant community and used the minirhizontron technology to investigate changes of root properties (standing crop, production, mortality, life span and turnover) in an alpine meadow, in response to five precipitation gradient, including 90%, 50% and 30% decrease (0.1P, 0.5P, 0.7P), ambient control (1.P) and 50% increase (1.5P). The results showed that: 1) There was no significant effect of precipitation gradient to above-ground biomass, while 0.5P and 0.1P significantly increased the biomass of grass (P<0.05). 2) The total root standing crop was not significant affected by treatments, but increased first and then decreased with precipitation decrease. There were significant differences in response of roots of different diameter classes among soil layers. In 0-10 cm soil layer, the standing crop significantly increased in 1-level roots under 1.5P and 0.7P, however, significantly decreased in 2 and 3-level. In addition, in 10-20 cm soil layer, the standing crop of 2-level roots in 1.0P was significantly higher than that in other treatment (P<0.05). 3) Root production of 1-level roots in the surface layer are significantly reduced under 0.1P, meanwhile, the total production and mortality of 1.0P in the surface layer was significantly higher than that of other treatments (P<0.05). 4) The life span of total roots and 1-level roots in the bottom layer increased under 0.1P (P<0.05). 5) Root turnover decreased with precipitation decrease, but there was no significant difference among treatments. 6) The structural equation model showed that the root standing crop and production were directly affected by the soil layer and water content, besides the root turnover was directly affected by the soil layer and nutrients. In summary, under small range of precipitation change (0.7P, 0.5P), plants would reduce the biomass allocation to fine roots and invest more resources in the growth of 1-level roots; however, under mild water stress (0.1P), the plant would reduce the allocation of underground root biomass in all diameter classes, maintain low biomass consumption and low root growth to maintain its normal growth state, so as to complete its normal ecological function.