Abstract: The dynamic cycle of carbon and carbon compounds is an important part of the coastal salt marsh evolution, and biogeochemical process is the main driving force to promote carbon cycle. This paper made a review on the carbon cycle in the coastal salt marsh soil. The carbon cycle is divided into the external and internal cycles in this paper. The external cycle means mainly the organic and inorganic carbon input and output, including the carbon budget in biogeochemical and mechanical processes, whereas the internal cycle includes aerobic and anaerobic mineralization and carbonate formation and storage. The burial of carbon is related to the long-term response to wetland evolution and sea level changes.