Forest productivity generally increases with tree species diversity. However, it is unclear how biodiversity of different trophic-level and interactions between tree species diversity and soil microbial diversity affect stand productivity. In this study, we selected plantations with different tree species richness and compositions in subtropical China, to investigate the effects of tree species diversity and soil microbial diversity on stand productivity, by using indicators of tree species richness, functioanl traits diversity, phylogenetic diversity as well as phylogenetic diversity of soil fungi and bacteria. The results showed that stand productivity increased significantly with tree functional diversity (FD) (P<0.001). Community weighted mean of specific leaf area (CWM-SLA) (P<0.01), phylogenetic diversity (PD) (P<0.05) and soil fungal diversity (PDF) (P<0.01), explaining 12.86%, 6.80%, 3.67%, and 3.08% of the total variance in stand productivity, respectively. FD and CWM-SLA can indirectly improve stand productivity by increasing the diversity of soil fungi and bacteria, respectively. Our findings suggest that pluritrophic biodiversity is conducive to maintain a high level stand productivity, and the top-down cascading effect between tree species diversity and soil microbial diversity plays an important role in shaping ecosystem productivity.