Compared with the grass individuals of alpine steppes community fenced for twenty years, the variation of morphological characteristic of four good herding grass species( Stipa purpurea, Agropyron cristatum, Poa pratensis, Artemisia scoparia) and three miscellaneous poison grass species (Dracocephalum heterophalum, Thermopsis lanceolata, Stellera chamaejasme) under grazing stress is studied, we find that the responses of good herding grass individuals to long-term grazing are not consistent with the responses of miscellaneous poison grass individuals. Good herding grass individuals show “Individual Miniaturization Phenomenon”, but miscellaneous poison grass individuals do not become miniaturized, especially for aboveground biomass. Different individual morphological variation results in the change of utilization ability to environmental resources, so the environmental spaces and resources (hypervolume niche) each population occupies in the community becomes “reshaped”, that of most good herding grass populations becomes "contracting " and it is "extending "for most miscellaneous poison grass populations, therefore the status of plant populations in the degraded grassland community changes, the dominant species alternates. This is the individual morphological principles of the degradation of alpine steppes community.