Abstract: The study of ecosystem processes associated with forest tree diversity and their stability under climate changes is the key to answering basic forest ecology questions and building theory framework. Deadwood is an important carbon and nutrient pool in forest ecosystems, and its decomposition process plays a key role in forest carbon and nutrient cycles and soil fertility. Climate change and frequent occurrence of extreme weather events have led to a continued increase in forest mortality, while the impact on carbon cycling will be exacerbated by a further increase in deadwood stocks in forests as forest management advances in the conservation of natural forests, harvesting of plantation forests and restructuring of forest stands. Currently, in order to improve the ecological quality of forests in China, forestry management agencies in many regions are carrying out the strict natural forest protection policy and transformation of forest stand structure, which will greatly increase the tree diversity. However, there is still a lack of research on how tree species diversity affects the decomposition and carbon cycling of forest deadwood, especially on the composition of soil microbial communities, and how soil microbes regulate the key processes of microbial colonization and decomposition in deadwood. Based on these gaps, this article reviews the effects of tree species diversity on soil microbial colonization processes, community composition, diversity and community succession in forest deadwood, discusses the metabolic processes of different microbial communities on deadwood decomposition and their responses to environmental changes, and explores the development of deadwood microbial decomposition models for predicting the characteristics of changes in the carbon pool of forest deadwood in China. Finally, the article suggests that in the future, we should strengthen the research on mechanism of microbial decomposition of deadwood and carbon sink effect of tree species diversity to improve the carbon sink capacity of forests, and at the same time, we should provide technical references for the improvement of quality of forest ecological services and the excavation of function of “carbon pool” according to current situation and future changes of the structure of China’s forest tree species.