The soil carbon reservoir, the largest terrestrial carbon pool, plays a critical role in regulating atmospheric CO₂ concentrations and climate change. Conventional research paradigms often treat soil organic carbon (SOC) and soil inorganic carbon (SIC) separately, limiting the predictive capability for soil carbon cycle dynamics. This review systematically synthesizes the formation and sequestration mechanisms of SOC and SIC. SOC stability is maintained by a complex "multi−assemblage" involving chemical recalcitrance, physical protection, mineral associated stabilization, and microbial regulation (e.g., the Microbial Carbon Pump, MCP). In contrast, SIC dynamics are governed by chemical precipitation−dissolution equilibria, biologically driven processes, and physical transport, with its perceived role evolving from a 'static geologic reservoir' to a 'dynamic carbon sink'. A key advancement is the revelation of deep biogeochemical coupling between SOC and SIC: CO₂ released from SOC decomposition drives the formation of secondary carbonates, while pH and Ca²⁺ concentration regulated by SIC dissolution, in turn, feedback on SOC stability and microbial activity. Building on this, we propose a novel "SOC−SIC−Climate" tripartite coupling framework, elucidating their dynamic pathways—including synergistic enhancement, trade−off compensation, and critical instability—under the forcing of external factors (climate, minerals, biology, human activities). Finally, translating mechanistic understanding into practice, we propose region−specific regulation and carbon management strategies (e.g., calcium cycle regulation, Microbially Induced Carbonate Precipitation (MICP)) tailored to different climate zones and land−use types. This aims to transform soil from a passive sink into an actively managed climate buffer, providing a scientific foundation for advancing Earth system theory and optimizing carbon neutrality pathways.