The vegetation community change and associated mechanism is one of the pressingly key scientific issues during soil desertification in the swamp area of the Zoigê plateau. Along soil desertification gradients, changes of species composition, species diversity and aboveground biomass and their relation to soil physical properties, i.e. soil moisture, volume weight and porosity, were studied in the desertified swamp area, Hongyuan County, the Zoigê plateau. As the increasing of the degree of soil desertification, the replacement order of community characteristic species group was Blysmus sinocompressus species group→Kobresia pygmaea species group→K. setchwanensi species group→Carex atrofusca subsp. minor species group→Kobresia robusta species group. Both the number of plant species (species richness per quadrate and total number of species) and above-ground biomass showed unimodal patterns. The highest number of plant species occurred in K. pygmaea community with extremely mild desertification, whereas the highest value of above-ground biomass occurred in K. setchwanensis-Carex atrofusca subsp. minor community with moderate desertification. The β diversity showed U-shaped pattern, which was the highest in Blysmus sinocompressus community with non-desertification, whereas the lowest in Kobresia pygmaea community with extremely mild desertification. Soil moisture was most correlated with the variation of plant abundance and explained 24.8% of total variance, followed by soil volume weight and explained 1.4%. Soil moisture was considered a key factor in regulating the ecological distribution and species assemblage of plant community during the process of desertification, especially for the abundance and distribution of characteristic species. K. robusta was considered a pioneer species of vegetation restoration in desertificated land in the Zoigê plateau.