Abstract: The Yangtze River Estuary is a crucial hub connecting land and ocean, characterized by its complex topography, abundant terrestrial material supply, and significant interaction with human activities, making it a focal point of scholarly attention. Research on the surface sediments of the Yangtze River Estuary and its adjacent seas provides comprehensive insights into the sedimentary environment and source-sink processes in this region, offering valuable information for understanding surface material cycles and exploring marine environmental evolution. This study focuses on the surface sediments of the seabed in the Yangtze River Estuary and its adjacent areas, systematically analyzing the geochemical behavior of Sr and Nd isotopes as well as trace elements. The results reveal that the sediments in the estuary and adjacent seas are primarily composed of terrestrial materials, with the majority originating from the Yangtze River Basin, and a portion from the ancient Yellow River Delta. Nd enrichment in the river-sea mixing zone is attributed to colloidal coagulation, while the complex hydrodynamic conditions lead to finer sediment particle sizes, and Sr exhibits significant depletion. Through the SIMMR (Stable Isotope Mixing Models in R) multi-source mixing model analysis, it was found that the contribution of materials from the middle and lower reaches of the Yangtze River to the surface sediments in the land-sea interaction zone has increased. The construction of dams in the upper reaches has significantly reduced sediment supply, turning the middle and lower reaches from a "sink" of sediment into a "source," thereby increasing their contribution to the estuary and adjacent seas. Despite this, materials from the upper Yangtze River still dominate the sediment composition in the estuary.