Mangrove wetlands, typical of wetlands in subtropic and tropic area, are considered as a huge carbon pool along the coast. In this study, typical mangrove wetlands in the north, east, south and west coasts of the HainanIslandwere selected for soil sampling. A total of 630 soil samples were collected from 126 sites, five soil samples each site from 5 soil layers, 20cm each, in 42 quadrats scattered in 14 mangrove communities. The samples were analyzed for soil organic carbon (SOC) contents with the potassium dichromate external heating method and SOC density was worked out based on soil bulk density. Through comparison between the sites in community structure, soil physical and chemical properties and natural conditions, exploration was done of regularities of the distribution of SOC in the mangrove wetlands and major factors affecting the SOC stock therein. Results show that the distribution of SOC content and density varied sharply with soil depth; the peak of SOC content appeared in 20~40cm, while that of SOC density did in 0~20cm; SOC content also varied with mangrove community; in the Dongzhai Harbor area, the Bruguiera sexangula community was the highest in SOC content (20.89±6.75 gkg^-1), while the artificial Sonneratia apetala community was the lowest (12.71±3.62 gkg^-1). Further correlation analysis shows that SOC content was positively related with DBH(diameter at breast height)of the mangrove trees and coverage of the community, but not with plant height. As to spatial distribution, a decreasing order of Simi Bay Dongfang ＞Qinglan Harbor Wenchang ＞Xinying Bay Danzhou ＞Dongzhai Harbor Haikou ＞ Sanya Bay Sanyawas observed. Finally, based on the area of the mangrove forests in HainanIsland, the mangrove forest soil in HainanIsland possesses a total stock of 2.39×106t organic carbon.