Using the mangrove plants and sediment of the typical mangrove areas in Guangdong's coastal areas, P. R. China as the research object, the density, storage and spatial distribution of carbon are studied. The study method is the combination of the wild field analysis and laboratory testing method. The results show that the carbon density of the sediment will gradually decrease because of the increased depth, and has nothing to do with the difference of the area and tree species. The average carbon density of 50cm sediment is 0.007gC/g. The carbon density is obviously different in different components of different mangrove species in different regions. The total carbon storage in different regions is in the following order: Zhuhai＞Gaoqiao＞Shenzhen＞Shuidong Bay＞Guanghai Bay＞Raoping＞Daya Bay＞Chenghai. The carbon density and carbon storage are obviously higher in mangrove covered area than blank area. It shows that mangroves have very strong carbon sink function.