Abstract: Grasslands dominated by Leymus chinensis in the west part of the northeast China and the eastern Inner Mongolia are the main natural pasture for grazing and hay production, and, therefore they are highly economically valuable. However, the degradation of these grassland ecosystem are very severe, mainly due to overgrazing.In this paper, we will use mathematical’models to show the change of the relative dominance of plant populations in the retrogressive succession series. In lightly and moderately grazed grasslands, Leymus chinensis is the dominance. Its relative dominance changes with increasing grazing intensity, and this change can be described by an equation, D=124.2e-0.35T2. In the entire succession series, the changes of the relative dominance of Carex duricscula and Cleistogenes squarrosa can be explained using models of D=2.13T3.3 e-0.15T2 (for C. duricscula) and D=1.77T3.7e-0.29T2 (for C. squarrosa). The relative dominance of Suaeda corniculata and Chloris virgata increases as the grassland degrades. Their relative dominance changes can be elucidated by the following models, D =0.11e1.3T (for S. corniculata) and D=0.38e10.94T (for C. virgata), respectively. Our results indicate that the shift of dominant species is very conspicuous during the retrogressive succession of grassland communities.