To investigate the contributions of microbial necromass carbon (MNC) and soil microorganisms to soil organic carbon (SOC) accumulation and their influencing factors during tropical rainforest restoration, soil samples from the layers of 0—20cm, 20—40cm, and 40—100cm were collected from secondary forests with varying restoration periods (30 years: ZH30, 45 years: ZH45, 75 years: ZH75) and a primary rainforest (YS) in Hainan Bawangling National Forest Park. The soil physicochemical properties, SOC, microbial community composition, fungal necromass carbon (FNC), bacterial necromass carbon (BNC), and the contributions of MNC to SOC were analyzed. The results showed: (1) SOC content in all soil layers initially increased and then decreased with restoration time, peaking in ZH75 (6.68—19.12g/kg) and reaching the lowest in YS (4.23—11.04g/kg), while declining with soil depth. (2) The contents of FNC, BNC, and MNC across restoration periods ranged from 1.51 to 4.55g/kg, 0.12 to 0.72g/kg, and 1.63 to 5.91g/kg, respectively. With increasing restoration time, BNC, FNC, and MNC significantly decreased in the 0—40 cm layers but showed no significant decline in the 40—100cm soil. Across the 0—100cm depth, FNC, BNC, and MNC generally decreased, with significant reductions observed in ZH30 and ZH45. The FNC/SOC, BNC/SOC, and MNC/SOC ratios in the 0—100cm layers were 18.9% to 58%, 1.1% to 11.1%, and 20.9% to 67.8%, respectively. In ZH30 and YS, the surface layers exhibited lower FNC/SOC, BNC/SOC, and MNC/SOC ratios than the subsoil, while ZH45 and ZH75 also showed similar trends. The BNC/SOC ratio significantly decreased in the 0—40 cm soil with restoration time but remained stable in the 40—100 cm soil. The FNC/SOC and MNC/SOC ratios followed the trend ZH30>ZH45>YS>ZH75 across all depths.(3) Correlation and redundancy analysis (RDA) revealed that litter quality and available phosphorus (AP) were key drivers of MNC accumulation. AP, available potassium (AK), and total nitrogen (TN) positively correlated with MNC, influencing its spatial dynamics. FNC dominated MNC contributions to SOC compared to BNC. Basidiomycota and Proteobacteria abundance positively correlated with MNC, while Verrucomicrobia negatively correlated with FNC/SOC and MNC/SOC. These findings suggested the critical role of long term vegetation restoration and microbial community composition in enhancing SOC sequestration in tropical rainforest ecosystems.