As a critical pathway mediating nutrient and carbon fluxes between plants and soil, mycorrhizal fungi can profoundly regulate soil organic carbon (SOC) dynamics by modulating plant carbon inputs, rhizosphere microbial processes, soil aggregate formation, and the decomposition and stabilization of organic carbon. A systematic synthesis of these regulatory mechanisms is therefore of great significance for deepening the understanding of terrestrial ecosystem carbon cycling, and for optimizing soil carbon sink management and climate change mitigation strategies. Based on recent advances in research on the relationships between mycorrhizal fungi and SOC, this review systematically summarized the roles of mycorrhizal fungi in regulating the input, decomposition, transformation, and stabilization of SOC, and proposed a conceptual framework in which mycorrhizal fungi affect SOC dynamics through three core pathways: plant-mycorrhizal interactions, enzymatic activity regulation, and mineral protection. The net effect of mycorrhizal fungi on SOC stocks depends on the functional direction and relative strength of these three pathways; however, their relative contributions remain difficult to disentangle quantitatively in current studies. Future investigations should integrate stable isotope tracing, molecular biomarkers, and model simulation approaches to quantitatively elucidate the processes of mycorrhizal fungal biomass turnover, necromass formation, microbial carbon use efficiency, and the formation of mineral-associated organic carbon, and should further incorporate mycorrhizal processes into ecosystem carbon cycle models. These efforts will improve the predictive capacity for the mechanisms underlying soil carbon sink formation and their responses to global environmental change.