Abstract: Sediment particle size characteristics are important parameters reflecting sedimentary environment. In order to understand the sedimentary evolution law of Fangchenggang Sea area, the authors carried out grain size analysis and ²¹⁰Pb isotope dating on five core sediments in the vertical coastline direction of Fangchenggang coastal waters, and obtained the grain size parameter change characteristics, sediment types and sedimentation rates of the five core sediments respectively. The Fangchenggang landform and human activities, the material source, sedimentation dynamics and sedimentation rate influencing factors were also considered. The results show that the variation range of grain size parameters of FC13Z, FC16Z and FC12Z above 60 cm is relatively small, indicating a relatively stable sedimentary environment. While, the variation range of grain size parameters of FC14Z, FC15Z and FC12Z below 60 cm is relatively large, indicating a relatively fluctuating sedimentary environment. The sediment sorting is relatively poor to poor, and the skewness is nearly symmetrical positive, with a very flat peak. The core sediments in the study area can be divided into seven types: sandy silt, silty sand, sandy mud, argillaceous sand, pebbly argillaceous sand, pebbly mud and mud. The sediment from the nearshore to the front edge gradually converts from sand dominated to mud dominated, and the sedimentation rate shows a significant weakening trend. The sediment source is mainly from river input and coastal erosion, and the sedimentary power mainly comes from tidal current and nearshore current system. The sedimentation rate is greatly affected by the tidal current. The results of this study would provide some references for the sedimentary environment and geomorphological evolution study in the coastal waters of Fangchenggang Sea.