Abstract: To understand the sedimentation and environmental characteristics in oyster reefs in Liyashan, Haimen, Jiangsu, vertical column sampling of sediments was carried out in 2023, from which the grain size statistical analysis, and ²¹⁰Pb and ¹⁴C dating of sediments were conducted. Results indicate that the substrate of the oyster reef consists of sandy silt and silt. The ²¹⁰Pb activity and excess ²¹⁰Pb_ex activity in core C01 exhibit a similar trend, characterized by a "decay layer–background layer" dual structure. In contrast, core C02 displays a "mixing layer–background layer" dual structure; the top 0–70 cm is the mixing layer, showing fluctuations in the activities, while below 70 cm, the activities remain relatively stable. The southern part of the study area is generally subject to erosion, while the northern part shows some siltation. Nearshore samples are influenced by the combined effects of coastal currents, tides, and tidal flows, resulting in stronger hydrodynamic conditions. In offshore areas, deeper waters and weaker tidal forces lead to less dynamic conditions and lower sedimentation rates. This study has important practical significance for local oyster reef protection and ecological restoration, as well as for the adjustment of the boundaries of protected areas.