Abstract: Grazing has significant effects on species composition and diversity of grasslands. Desert steppe is highly sensitive to the variations of precipitation. Based on a multi-year grazing experimental platform of Stipa breviflora desert steppe in Inner Mongolia, we investigated species composition and its quantitative characteristics and explored the effects of abnormal precipitation on species richness and dominance under different stocking rates. The results showed that a total of 50 species were recorded in the research site, of which 48 species were recorded in wet year and 29 species in dry year. The community quantitative characteristics and species richness in wet years were significantly higher than those in dry year, while the dominance of S. breviflora in wet year was significantly lower than that in dry year. The community quantitative characteristics decreased with increasing stocking rates. Species richness had a linear negative correlation with stocking rate, but a nonlinear positive correlation with precipitation. The dominance of S. breviflora had a linear positive correlation with stocking rate, and a nonlinear negative correlation with precipitation. Species richness had a linear negative correlation with the summed dominance ratio of S. breviflora. Both abnormal precipitation and grazing had significant impacts on species richness and dominance in desert steppe. Light grazing was beneficial to maintain plant species richness. This study provides basis for scientific management and rational grazing in desert steppe.

Key words: stocking rate, species richness, summed dominance ratio, abnormal precipitation, desert steppe.