Abstract: The spatial distribution characteristics and sources of organic carbon in sediments are a key issue in the study of salt marsh carbon cycling. The study analyzed the parameters of total organic carbon (TOC), total nitrogen (TN) and stable carbon isotope (δ13C) in the surface sediment samples of the Chongming Dongtan salt marsh in the Yangtze River estuary. The results showed that the average TOC and TN in surface sediments in Dongtan were 7.70±3.74 g/kg and 0.74±0.32 g/kg respectively. Both showed a decreasing trend from the northern part of the salt marsh to the south of the salt marsh in content. The average value of sediment δ13C was-25.05±1.21‰. The simulation results of the three end-member mixing equations showed that the organic carbon in Dongtan sediments was mainly derived from suspended particles (43.53±22.44%) and vegetation (43.29±24.82%). The contribution rate of microalgae is lower (13.20±8.40%). The sediments in the northern part of Dongtan are characterized by high organic carbon content, in which the contribution of suspended particulate matter is high and the contribution of vegetation is low. In the middle and south, the content of organic carbon is low, the contribution of suspended particulates is low and the contribution of vegetation is high.