Abstract: Carbon dioxide (CO₂), a main component of greenhouse gases, whose discharge is continually increasing with the development of modern industrialization. More and more attention has been drawn to the " energy-saving", " ejection-decreasing", carbon source and carbon sink, as the Kyoto Protocol came into force on Feb 16, 2005. The ocean, which covers more than 70% of the earth, is the biggest carbon sink, accounting for 93% of the total carbon in the earth, 50 times as that of atmosphere. The processes of solubility pump (SP) and biological pump (BP) driven by carbonate systems or planktons are important carbon fixation mechanisms in ocean. The concentration and global circulation of CO₂ are significantly affected by these processes. The coastal waters are significantly influenced by human activities, especially the mariculture activities greatly affect the coastal carbon cycling and carbon sink capacity. This paper reviews the carbon source, carbon sink and ocean-carbon-fixation mechanisms, and discusses the development of carbon sink fisheries in South China Sea.