Abstract: Based on the chronological framework established by ²¹⁰Pb, the development of mangrove forests over the past 100 years was reconstructed by analyzing total organic carbon (TOC) , total nitrogen (TN) , stable carbon isotope (δ¹³C) , and particle size indicators in sediment core S of Trat Province, Thailand, and the main influencing factors were discussed. The results showed that the TOC content in sediments ranged from 2.65% to 9.35%, gradually increasing from bottom to top; The range of δ¹³C value variation is −28.53～−25.46 ‰, showing a negative shift trend from bottom to top. According to the end-member mixing model, the contribution of organic carbon sources is quantitatively calculated. The contribution of organic carbon in this region is mainly from terrestrial and mangrove sources, with relatively small contributions from marine sources. The development of mangrove forests in Trat Province over the past 100 years has been mainly influenced by air temperature, rainfall, and human activities, with relatively little impact on regional hydrodynamics. From 1948 to 1962, human activities were relatively weak, and with the increase of air temperature and rainfall, the contribution of organic carbon from mangrove sources gradually increased. During the period 1962-2004, Marine aquaculture activities increased, and nutrient emissions from aquaculture stimulated the growth of mangrove forests. The deforested mangrove branches and leaves deposited in situ promoted the accumulation of mangrove-derived organic matter. Since the Indian Ocean tsunami in 2004, mangrove has played a prominent role in wave prevention and disaster reduction. The Thai government has carried out large-scale mangrove planting. With the expansion of mangrove area, the contribution of mangrove-derived organic matter in sediment continues to increase.