The effects of global changes on grassland ecosystems have become a focus of great concern in the whole world due to natural factors and human activities. The ecological effects of global changes, including elevated CO_2, warming, and increased nitrogen deposition, on grassland ecosystems are complex. The responses of the grassland vegetation and soil environment of plant-site interface to global changes are very sensitive, and there is a close relationship between soil microbial communities and the plant-site interface of grassland ecosystem. The response mechanisms of microorganisms to global changes differ from different levels. The factors of climate changes have direct or indirect effects on soil microorganisms, but the mechanisms are still not clear. The effects of global changes, including elevated CO_2, warming, and increased nitrogen deposition, on the soil microbial community diversities of grassland ecosystems and the response mechanisms of grassland microorganisms to global changes are reviewed in this paper. And the issues and research trends are discussed.