Plant root system architecture (RSA) is one of the most important characteristics of plant morphology. RSA exhibits a plasticity that is not only controlled by genetic factors but is also regulated by diverse environmental factors. Recently, a large number studies have indicated that rhizosphere microorganisms can regulate the plant RSA, and further influence an array of plant physiological and ecological processes. This paper mainly reviews the regulation patterns and corresponding mechanisms of plant RSA mediated by the important rhizosphere microorganisms, such as arbuscular mycorrhizal fungi, rhizobia, and plant growth-promoting rhizobacteria. Future research is proposed to provide reference for related research and practical applications.