Functiona1 diversity of soil microbia1 communities in rhizosphere of Caragana microphylla, a dominant shrubby leguminous species in the Inner Mongolia Grassland Ecosystem, was examined using the Biolog method to evaluate the effects of environmental changes in atmospheric CO2 concentration, soil nitrogen level and water level on soil microbia1 community. The results showed that total amount of carbon sources utilized by microbes in rhizosphere of C. microphylla increased with the incubation time. The main types of carbon sources utilized were polymers, carbohydrates and amino acids. Principal Component Analysis indicated that microbial community functional diversity varied significantly among 8 treatment groups. Fourteen categories of carbon sources were significantly related to the principal component 1, which belonged to polymers, carbohydrates, amino acids, and carboxylic acids. Elevated CO2 significantly increased the value of average well colour development (AWCD), richness index and Shannon evenness. Under nitrogen addition treatments, AWCD, richness index and Shannon evenness were significantly decreased, but this inhibition was slightly alleviated under elevated CO2. Water addition showed no significant effect on AWCD and diversity indices of soil microbial community. Rhizospheric microbial activity were higher under combined treatments of elevated CO2 and nitrogen addition than CK, which implied that the positive effect of elevated CO2 on microbial activity of C. microphylla was larger than the negative effect of nitrogen addition on it. There was significant CO2 nitrogen interaction on AWCD, richness index and Shannon evenness. In conclusion, microbial community functional diversity in rhizosphere of C. microphylla was sensitive to environmental changes, with the sensitive carbon source types being polymers, carbohydrates, amino acids, and carboxylic acids, essentially those carbon sources that are also the most heavily used.