Coastal wetland ecosystems have a great capacity to store carbon (C), and the condition has a significant influence on carbon emissions and segregation. This study aims to estimate carbon stocks in both vegetation and soil of coastal wetland ecosystems, and to compare the C stocks of different ecosystems and soil layers. This study classified coastal wetland ecosystems into six types, and C stocks were quantified through the measurement of vegetation biomass and soil C. The C stocks of estuaries, muddy beaches, coastal saltwater lakes, mangroves, deltas, and seagrass beds were 210.73, 243.00, 167.41, 426.57, 185.88, and 297.85 MgC ha^-1, respectively. Mangroves were found to be the most carbon-rich ecosystem. The total organic C content (TOC) of soil decreased with soil depth and was the highest in the top 0-20 cm layer. The total C storage of coastal wetland ecosystems in Hainan Island was 56.51×10⁵ Mg of C. These estimates show that there is an urgent requirement to protect coastal wetland ecosystems.