Grasslands, such as tree-scattered grassland, sandy grassland, semi-shift sand land and shift sand land, were obviously in a series of degradation stages of Horqin sand land. Each stage was dominant of a species. Moreover, role of the dominant species in every community was prominent for its performance of the most functions of the community. In the early stage of grassland degradation, tree-scattered grassland had a high diversity and relatively stabile community structure, and the species richness, diversity, grass and family number were continually decreased with degradation and/or desertification of grassland. The annual and biennial herbs and xerophytes were dominant in every degraded stage of grassland, and played important roles in maintaining stability and ecological function of the community. The changes of species and functional groups that resulted from mutual interaction between species adaptability and environment, in degraded process of grassland, showed a series of trends in vegetation and environment, such as ecosystem degradation, simplification of community structure, decreased stability of environment matrix and so on.