The experiment was conducted in pot with ‘Wuchuan’ and ‘Hunyuan’(biennial Astragalus mongholicus at greenhouse in Inner Mongolia University.The dynamic of rhizosphere microbial quantity and biomass on the two cultivars under continuous drought was studied through artificially controlling soil water content to stimulate drought condition.The results show that there are the obvious differences in bacteria,actinomycetes and fungi,and the microbial flora composition is dominated by bacteria,and then actinomycets .And along with continuous drought stress,bacteria and actinomycete amounts in the rhizosphere soil of two cultivar A.mongholicus first increased then decreased.However,the fungus amounts in the rhizosphere soil of A.mongholicus decreased continually comparing to the control.At the same time,the growth of A.mongholicus was inhabited by drought stress.The biomass in aboveground and roots parts of two cultivars A.mongholicus,root and leaf tissue relative water content all declined but R/S-ratio increased with the increase of drought intensity.Correlation analysis showed that the number of rhizosphere soil microbe had a significant positive correlation with aboveground biomass,but weak relation with roots biomass.The results indicated that the moderate drought improved the quantities of bacteria and actinomycetes,thereby altering the microbial community structure ,which is beneficial to the accumulation of aboveground biomass of A.mongholicus.