Abstract: The alpine grassland desertification has seriously affected the species composition of vegetation and species diversity,and vegetation plays an irreplaceable role in human and animals living environment. In this paper,the typical alpine desertification grassland areas were selected in northwest Sichuan as the research area, such as Ruoergai, Hongyuan, Aba,Seda, Daocheng and Litang counties, and studies were made of their vegetation characteristics and species diversity with different desertification degree. The results showed that with the development of the desertification, the plant species also presented a trend to increase firstly and then decrease, and the dominant species displayed a continuous succession. Gramineae and Cyperaceae plants decreased gradually,and were replaced by Asteraceae and Rosaceae plants; Species diversities were lower in exposed sandy and shifting sandy land than those in half-fixed sandy land and fixed sandy land. β_T and C_N diversity index presented an opposite trend, the difference of plant communities was in different desertification stress at the beginning, but they were ultimately determined by various environmental and biological factors together.