【Objective】Masson pine forest (Pinus massoniana Lamb.) is a typical ectomycorrhizal (ECM) dominant forest. However, in recent years, the ecological service function of the Masson pine forest decreased due to pine wood nematode disease, and the Masson pine forest was gradually replaced by an Arbuscular mycorrhizal (AM) dominant broadleaved forest. However, it remains unclear what influence could be exerted by the changes of dominant mycorrhizal types on soil organic carbon accumulation during the conversion of Masson pine forest to broadleaf forest in the subtropical region. 【Method】In this study, the biomass of ECM fungi and AM fungi were determined by high-performance liquid chromatography (HPLC) and neutral lipid fatty acids (NLFA), respectively. At the same time, phospholipid fatty acids (PLFAs) technology was used to study the characteristics of the microbial community. The content of glomalin-related soil protein (GRSP) and the activities of soil extracellular enzymes was also determined in Masson pine and broadleaved forests in Jiande County, Zhejiang Province.【Result】The results showed that: AM fungi-dominated (AMD) broadleaved forest replaced ECM fungi-dominated (ECMD) Masson pine forest, soil organic carbon in AM fungi dominated broadleaved forest was significantly enhanced by 36.81%, microbial carbon use efficiency (CUE) significantly increased by 53.85%, and AM fungal biomass significantly increased by 25.57%. Moreover, compared with ECM fungi-dominated forests, the biomass of ECM fungi in AM fungi-dominated forests decreased significantly by 45.04%. The Masson pine forest, which was dominated by ECM fungi, was subjected to more severe microbial nitrogen limitation. Phospholipid fatty acids analysis showed that the gram-positive bacteria (G⁺) and the ratio of gram-positive bacteria to gram-negative bacteria (G⁺/G^-) in Masson pine forest dominated by ECM fungi compared with the broadleaved forest dominated by AM fungi were significantly decreased by 21.47% and 6.46%, respectively. Redundancy analysis (RDA) results showed that there were significant differences in microbial community structure between forests dominated by AM fungi and ECM fungi (P<0.05), in which AM fungal biomass (R²=0.48, P=0.002) and soil organic carbon content (R²=0.47, P=0.003) were significantly correlated with the variation of microbial community structure (P<0.05).【Conclusion】The decrease of GRSP and the different recruit of microbial groups by different mycorrhizal fungi types were important reasons for the reduction of soil organic carbon content in forests dominated by ECM fungi compared to AM fungi dominated forests. Therefore, the substitution of broadleaved forest for Masson pine forest in the subtropical region increased the content of forest soil organic carbon and improved the function of the forest carbon sink.