Forest is an important component of terrestrial ecosystems. Its high productivity and ecosystem services play a key role in anthropogenic survival and development. The increases in forest tree species diversity can significantly increase forest productivity. It has been widely concerned about how tree species diversity influences the belowground biodiversity and ecosystem functioning. From the perspective of soil microorganisms and their mediated biogeochemical cycling of elements, we reviewed the effects of tree species diversity on soil bacterial and fungal diversity, community structure and ecosystem functioning, and further proposed future research directions. In general, tree species diversity is beneficial to increase soil bacterial biomass and diversity. Tree species diversity is an important bio-indicator of the diversity and community structure of pathogenic fungi and mycorrhizal fungi. Tree species diversity can increase soil organic carbon storage, and enhance soil methane oxidation capacity, as well as facilitate soil phosphorus turnover and bioavailability. The relative contribution of diversity hypothesis and mass ratio hypothesis should be taken into consideration in terms of the effects of tree species diversity on the nitrogen cycling. In the future, we should devote great efforts to the influence of tree species diversity on interactions among multiple trophic levels. Meanwhile, more attention should be paid to the effects of tree species diversity on ecosystem multifunctionality. Interdisciplinary research and modelling prediction methods, such as microbial population dynamics model and climate model, should be incorporated to explore the mechanisms of tree species diversity in response to global environmental change. This aims to promote the study on the relationship between aboveground plant diversity and belowground ecosystem functioning, and thus enhance the capacity of forest ecosystem for dealing with future global environmental change.