Abstract: The heterogeneity of plant community species composition is the main attribute of plant community dynamics. By using line transect and quadrat methods, and based on species frequency and power law, this paper analyzed the variations of plant community species composition and spatial heterogeneity in an Inner Mongolian Stipa krylovii steppe under exclosure and uncontrolled grazing conditions. Inside and outside of the exclosure, the plant species all presented a centralized distribution. In terms of functional groups, xerophytes and mesoxerophytes were widely distributed inside and outside of the enclosure. Perennial herbaceous species dominated in life form. More than 60% of the species spread their seeds by gravity. Gramineae, Liliaceae, Compositae, and Leguminosae had a comparative advantage. Under exclosure, species diversity increased while community heterogeneity decreased, suggesting that the degraded grassland due to grazing was changing better.