Abstract: Located in the transitional zone between marine and terrestrial ecosystems, coastal wetland has extremely high productivity and photosynthetic carbon sequestration efficiency, which is an important part of the coastal blue carbon sink. The productivity of coastal wetlands depends not only on terrestrial vegetation such as reed, seablite and mangrove, but also on photosynthetic carbon fixation of phytoplankton in water. However, more studies in the past focused on terrestrial vegetation, and few reports on phytoplankton and benthic microalgae in coastal wetland waters. In recent years, the carbon cycle and carbon sink process of the multi-sphere ecosystem of coastal wetland have become research hotspots with the attention from governments and scientists to carbon dioxide emissions and climate change. As a key link of the multi-sphere carbon cycle, the productivity and photosynthetic carbon sequestration in wetland waters should be paid more attention. In this paper, the coastal wetland of Liao River Delta, a typical salt marsh region in northern China, was taken as a case study to review the research progress of wetland water productivity and discuss its influencing factors, to provide a reference for fullfilling the national carbon cycle and carbon neutralization commission.