Achnatherum splendens is a constructive species in arid or semiarid grassland, vegetation composition and community stability of its community can affect the desertification degree of grassland, which represents successional dynamics and development direction of community. The aims of this study is to explore the relationship between vegetation composition, interspecific association and community stability by analyzing the composition, and diversity of species, functional group biomass composition, Raunkiaer frequency coefficient, and Spearman rank correlation of A. splendens and Stipa communities in Songshantan grassland in Gansu Tianzhu. The results indicated that, (1) the species diversity of Stipa community was richer than that of A. splendens community，and the degree of species replacement was similar in these two communities. (2) The two communities were degraded, with the grassland degradation increased, A. splendens and Stipa communities dominated by grasses and forbs, respectively. (3) The positive to negative association ratio of speciespairs in two communities was less than one, and the interspecific association was loose, and they had a low community stability. (4) The high species diversity was not benefit for the stability of Stipa community. The study suggests that biomass composition of functional group, evenness of species and drought disturbance had higher effects on the community stability than that of the species diversity.