Considering climate change, coastal mangroves are facing serious threats from rising sea levels. However, whether the largest contiguous Dongzhaigang mangrove in China can adapt to future sea level rise, which is very critical for mangrove restoration and management, has been little known. Using the data of historical monitor since the 1950s, supplementary field research of mangrove wetland sediment rates measured, satellite remote sensing, digital elevation model, global climate models, and ArcGIS, we investigated the Dongzhaigang mangrove area changes, related causes, and the impacts of future sea level rise under greenhouse gas emission scenarios, as representative concentration pathways (RCPs) 2.6, 4.5, and 8.5. The study revealed that: (1) during 1956–1987, total mangrove area had decreased by ~ 50%, from ~ 3417 hm2 to ~ 1710 hm2. This was mainly because of the impacts of human activities, such as fish pond reclamation and the use of former mangrove land for economic tree planting. After the 1990s, the total mangrove area was maintained at ~ 1711 hm2, mainly because of the establishment of the nature reserve in 1986, along with protective and restorative measures; (2) under the intermediate and high RCP 4.5 and 8.5, sea level increases are likely to cause > 25% of the mangroves to disappear by 2100, whereas for the low RCP 2.6, only 17% of the mangroves are likely to be affected; and (3) taking measures such as reestablishing ponds as mangrove forests, plant restoration, and biological shore protection could improve the adaptation of mangroves to the impacts of rising sea levels.