Flooding　is　one　of　the　key　environmental　factors　affecting　the　carbon　sequestration　potential　of　estuarine　tidal　flat　wetlands.　In　order　to　reveal　the　effect　of　flooding　on　soil　carbon　(C)　sinks　in　estuarine　tidal　wetlands,　we　investigated　and　analyzed　the　soil　organic　carbon　(SOC)　storage,　the　contents　of　active　SOC　components,　and　SOC　stability　indicators　across　a　tidal　flat　in　the　Jiulong　River　estuary　in　southeast　China.　The　results　showed　that　the　SOC　storage　gradually　decreased　by　54%　with　the　increase　in　flooding　frequency.　The　change　pattern　of　microbial　biomass　carbon　(MBC),　dissolved　organic　carbon　(DOC),　and　liable　organic　carbon　(LOC)　followed　the　change　pattern　of　the　SOC　storage.　With　the　increase　in　flooding　frequency,　DOC/SOC　and　LOC/SOC　increased　by　80%　and　26%,　respectively,　whereas　MBC/SOC　decreased　by　29%.　As　flooding　frequency　increased,　particulate　organic　carbon　(POC)　and　mineral-associated　organic　carbon　(MAOC)　contents　decreased　by　81%　and　35%,　respectively.　The　decreases　in　POC　contents　were　correlated　with　the　increases　in　soil　pH,　whereas　the　decreases　in　MAOC　contents　were　associated　with　the　decline　in　clay　contents.　Soil　carbon　stability　index　(CSI)　increased　by　246%　with　increasing　flooding　frequency.　These　combined　results　indicated　that　SOC　storage　decreased,　but　SOC　stability　increased,　with　the　increased　flooding　frequency.　Mineral-bound　organic　carbon　was　the　main　protection　mechanism　for　the　SOC　stability,　which　was　of　great　significance　to　the　soil　C　sink　of　the　estuarine　tidal　wetlands.　©　2022,　Science　Press.　All　right　reserved.