Two types of typical steppe ecosystems in Mongolia (dry steppe and mountain steppe) with two treatments (enclosure and grazing) were studied to analyze the vegetation cover from 2013 to 2018. The plant species of the community were divided into five functional groups: forbs, artemisia, legumes, grasses and sedges. The Gordon stability index was used to evaluate the effect of enclosure on the community stability. Here are the results. 1) Enclosure significantly increased the coverage of forbs in the dry steppe, while reduced the coverage of artemisia and gramineous groups. The effects had no obvious variations among years. For the mountain steppe, enclosure slightly affected the coverage of different functional groups. 2) Enclosure increased the stability of the dry steppe while little influenced the stability of the mountain steppe. 3) The Gordon stability index had a significantly positive relation with the cover ratio of dominant species to the communities. The ratio in the dry steppe was higher than that in the mountain steppe, leading to a higher community stability of the dry steppe. Before the enclosure management in grasslands, we should fully consider local environmental conditions and the potential impact of enclosure on the plant community and the ecosystem. At the same time, grazing rest, rotational grazing, seasonal grazing and other measures should be supplemented to improve the use value of grassland ecosystem services.