Abstract:Abstract The investigation shows that the Stipa genus in its narrow sense has only two species, Stipa baicalensis and S. grandis, on the Song-Nen Plain. The Stipa Steppe constituted by them mainly has four community types: ( 1 ) Stipa baicalensis community; ( 2 ) Stipa baicalensis and Filifolium sibiricum community; (3) Stipa grandis and Stipa baicalensis community and (4) Stipa grandis community. Through the analysis of the geographic distribution and the ecological environment of the two species of Stipa, the flora composition, the species composition of the communities, the characteristic of community structure, the eco-geographical distribution pattern of varies types of Stipa Steppe, and the differences of the water and soil conditions which they reflected, it can be confirmed that the Stipa baicalensis community is the representative zonal vegetation of this region and it should be put under the meadow-steppe in the regionallsation of Chinese temperate grassland, be separated from the steppe which distributes in the Inner Mongolia Plateau, and be considered as an independent natural region.