Abstract: Effect of the population densities of plateau zokor (Myospalax baileyi) in six density grades selected in alpine meadow of Haibei,Qinghai Province on biomass,structure and succession of plant communities was examined quantitatively with data collected in May and August of 1995 and 1996.Species composition,biomass,recovering rate of plants after be covered by mounds among six grades showed strong changes.The species numbers,total biomass of aboveground and monocotyledon biomass showed significantly negative correlation with population density,respectively.However,there was significantly positive correlation between the population density of plateau zokor and the log value of bicotyledons percentage of total biomass.As the population density of plateau zokor increased,the importance value of monocotyledons decreased significantly.However,some bicotyledons which contain second chemical compounds increased rapidly,the importance value of some plants which have strong roots became the biggest in plant community while zokor density was in the middle grade.The important value and biomass of grasses increased significantly,but the biomass of total plants didnt increase after some of zokor population were removed.