Abstract: Currently, about 25% of CO₂ from fossil fuel sources has been absorbed by the oceans, which mitigated the impact of human activities on climate change. The oceans transported CO₂ from the atmosphere to the deep sea through several conceptual carbon pumps. The high pressure and low temperatures of the deep sea could facilitate the dissolution of CO₂, and the oceans have stored inorganic carbon equivalent to 50 times of that in the atmosphere currently. Besides, the large amounts of methane hydrates have been stored in deep-sea sediments. Understanding the carbon cycle process in the deep sea is important to protect the carbon sequestration capacity and develop the carbon sequestration potential of the ocean. The authors have summarized the domestic and international researches on ocean carbon reservoirs and carbon deliveries, focusing on the process of the carbon cycle in the deep sea and the impacts of high pressure on life activities. The microorganisms drive the deep-sea carbon cycle, and the most of the organic carbon containing in phytoplankton is mineralized to CO₂ by microorganisms during sedimentation or converted to refractory organic carbon, which makes the deep sea to be a vast and long-turnover time reservoir of organic carbon. The high pressure could increase the activity of archaeal methane anaerobic oxidation and enhance the ability to shield methane release from the seafloor. Besides, the process of methane oxidation under high pressure produces bicarbonate, and acetic acid which can support heterotrophs, so the global budget of methane anaerobic oxidation may be underestimated. The additional production of ammonia from cellular metabolism under high pressure could serve as a potential energy source for inorganic carbon fixation by ammonia-oxidizing archaea. Therefore, it is urgent for deepening our understanding of the deep-sea carbon cycle and other elemental cycles to investigate the impact of present and future human activities on deep-sea carbon cycle processes and environmental effects, and to assess the possibility of applying the deep sea as a geoengineering technology platform to sequester CO₂.