According to depth, the South China Sea can be divided into three boxes by pycnocline and sill.When sea water rises to Box Ⅰ, dissolved inorganic carbon in water can be changed into particulate organic carbon by the organisms assimilation.One part of the particulate carbon will be changed into dissolved inorganic carbon, other will fall down to Box Ⅱ.The similar process eeds in Box Ⅱ and Box Ⅲ and the unresolved particulate carbon in Box Ⅲ will setth into sediments, finally.