ABSTRACT Understanding how litter diversity and soil fauna drive microbial communities is critical for revealing trophic cascades in decomposition processes. We conducted a 460‐day field decomposition experiment in a subtropical forest, placing litter mixtures of one to four tree species into mesh bags with 25 μm or 4 mm openings to create fauna‐excluded and fauna‐accessible treatments, and assessing microbial community composition and biomass using phospholipid fatty acid (PLFA) analysis. The results showed that the litter traits and diversity significantly influenced microbial PLFA content. Both fungal and bacterial PLFA content increased with higher levels of nitrogen, phosphorus, manganese, potassium, and leaf thickness in the mixed litter. Soil fauna had a significant impact on microbial PLFA content and its community distribution. A notable interaction between soil fauna and litter richness was observed: soil fauna slowed the decline of bacterial PLFA content as litter richness increased, highlighting their role in moderating the impact of litter diversity on microbial communities. Additionally, soil fauna reversed the relationship between mixed litter traits and arbuscular mycorrhizal fungi (AMF) PLFA content. While a negative correlation was observed in the absence of soil fauna, their presence turned it positive, demonstrating that soil fauna modifies the impact of litter traits on AMF. These findings demonstrate the intricate interactions between plant litter diversity, soil fauna, and microbes, highlighting the crucial role of soil fauna in modulating the effect of plant diversity on microbial communities during decomposition.