Abstract: Soil, one of the largest carbon reservoirs in the ecosystem, has substantial storage capacity and significantly affects global climate change. Currently, most studies on soil organic carbon storage and turnover focus on topsoil organic carbon (0−1 m) (SSOM), whereas systematic studies on the storage, stability and responses of subsoil organic carbon (DSOM) below 1 m to human activities are relatively limited. This study comprehensively reviewed the latest studies focusing on the storage, sources, composition, stability, and human activity responses to DSOM. Globally, the storage of subsoil organic carbon ranges from 29.9 to 219.6 t·hm⁻², accounting for 15%−84% of the total soil organic carbon storage. The average age of the DSOM is between 4800 and 28 100 a, with a turnover time spanning from 1000 to 4285 a. The stability of DSOM is significantly higher than that of SSOM, mainly due to the anaerobic environment, mineral protection and chemical inertness of DSOM. The key factors affecting the stability of DSOM include excessive fertilization, changes in cropping systems and fluctuations in groundwater levels. Although the mineralization rate of DSOM is significantly lower than that of SSOM, human activities, such as nitrate leaching due to excessive nitrogen fertilizer application, changes in cropping systems and groundwater level fluctuations, have significantly reduced the stability of DSOM in some regions, potentially having a profound impact on global climate change. The substantial storage potential of DSOM for carbon sequestration is comprised by these activities, which may lead to the release of stored carbon back into the atmosphere, thereby exacerbating global warming. Previous studies indicate that the substantial storage of DSOM has significant potential for carbon sequestration, and human activities may have comprised its stability, potentially leading to profound effects on global climate change. Therefore, investigating the DSOM is crucial. However, the underlying mechanisms and processes have not been fully explored, and further comprehensive research is required. Future studies should focusing on 1) assessing the storage and stability of regional / global subsoil carbon pools, 2) clarifying the mechanisms by which subsoil organic carbon pools responding to human activities, and 3) quantifying the contribution of human activity-induced subsoil organic carbon release to global warming. These research directions are essential to fully understand and leverage the role of DSOM in climate change mitigation and ensure the sustainability of our planet for future generations. In summary, the study of DSOM is at the vanguard of soil science and global change research, necessitating a multidisciplinary convergence of pedology, geochemistry, microbiology and environmental science. Advancing our understanding of DSOM is the key to harnessing its capacity as a natural climate change mitigation tool and securing the planet’s sustainability for future generations.