Desert grassland ecosystem was significantly effected by the grazing and abnormal precipitation, resulting in the composition and diversity of plants posed changes under the variation of precipitation and stocking rates. However, the response mechanism of species is not yet clear in the desert steppe. In this study, the composition and diversity of plants were investigated in the Stipa breviflora desert steppe of Inner Mongolia under different stocking rates (CK, without grazing, light grazing[LG, 0.93 sheep unit hm^-2half·a^-1], moderate grazing[MG, 1.82 sheep unit hm^-2half·a^-1], heavy grazing[HG, 2.71 sheep unit hm^-2half·a^-1]) to reveal the effects of precipitation and grazing on plant communities. The results indicated that (1) the increase of precipitation significant improved the community quantitative and diversity of species, but has a greatly inhibitory effect on the species dominance index, (2) it also enhanced the number of species with different functional attributes, but reduced the Stipa breviflora summed dominance ratio (SDR) and lead to the variation of composition and diversity of community species, and (3) the synergistic and mutually restrictive changes were found between precipitation and stocking rates and the C3 plants and total density were major affected by the stocking rates, which indicated the responses to stocking rates varied among species under different functional attributes. The abnormal precipitation can affect the ecosystem process that influenced by a long-term overgrazing and has a positive effect on the restoration of the grassland ecosystems.