The species richness of woody plant was investigated in an area desertified at different gradients in Beipan River Basin of Guizhou Province via the method of cluster analysis, and the adaptive capability of different tree groups was clarified according to the desertification of their habitat. The study results indicated that: (1) the biodiversity expressed in families, genera and species decreased with the desertification extent increasing. In specific, desertification increased the species number of the deciduous plants, the nanophanerophyte and the microphanerophyte, but decreased the evergreen plants, the mesophanerophyte and the megaphanerophyte. (2) Forty six dominant species were divided into 8 functional groups when the Euclid Distance equaled 6.5. There were 3 functional groups with 21 tree species in the area slightly desertified, 3 functional groups including 14 tree species in the medium desertified area, and 2 functional groups including 10 tree species in the heavily desertified area.