The diversity of partners in mycorrhizal associations shapes the ecosystem processes and functions. Mycorrhizal fungi and host plants tend to develop in patterns with mutual preference or specificity, which may induce differential benefits to the host plants by diverse fungi, and discrepancies of promotion to the fungi by their plant partners simultaneously. In the process of mutualistic symbiosis, both plants and fungi select their potentially favorable partners and incorporate each other along with facilitative and antagonistic relationships (such as complementarity, selection, and competition), and thus driving the ecosystem development and evolution. This review summarized the mutual effects between mycorrhizal fungal diversity and plant diversity, discussed the presumable regulating factors and the underpinning mechanisms of their correlations, and pinpointed several future research directions based on the concerns in understanding such complicated relationships. Further studies to demystify such interacting relationships between mycorrhizal fungal diversity and plant diversity, will advance our knowledge and understanding on the symbiosis, and also help promote the application of mycorrhizal technologies and sustainability of biodiversity.