Abstract: Based on the test results of grain size and major elements of surface sediment samples from 44 stations inside and outside the Swan Lake in Rongcheng, the plane distribution characteristics and differences of grain size and major elements inside and outside the lagoon were analyzed. Combined with correlation analysis, hydrodynamic numerical simulation, cluster analysis, principal component analysis and other methods, the main control factors of the distribution of major elements were explored. The results show that the sediment components of Swan Lake are mainly sand, and the sediment components of Rongcheng Bay are mainly silt. The grain size of Swan Lake sediment is obviously coarser than that of Rongcheng Bay. The average contents of SiO₂ and P₂O₅ in the sediments of Swan Lake (75.74 and 0.055%) were higher than those in Rongcheng Bay (61.73 and 0.053%), and the contents of major elements such as Al₂O₃, TFe₂O₃ and MgO were lower than those in Rongcheng Bay. On the whole, the distribution of SiO2 is opposite to the distribution trend of average particle size, and the distribution of most other major elements is similar to the distribution of average particle size. The content of most major elements in Rongcheng Bay gradually increases from the shore to the open sea, and the content of Swan Lake gradually increases from the shore to the lake. Particle size is the main factor affecting the distribution of most major elements (SiO₂、Al₂O₃, TFe₂O₃, MgO, etc.) in Rongcheng Bay and Swan Lake, and its impact on Rongcheng Bay is significantly higher than that on Swan Lake. The distribution of K₂O in the sediments of Swan Lake is affected by the erosion material and grain size of Chengshantou coast, and the distribution of K₂O in Rongcheng Bay is mainly affected by the erosion material. The distribution of P₂O₅ in the sediments of Swan Lake is mainly affected by human activities and seagrass beds, while the distribution of P₂O₅ in Rongcheng Bay is mainly affected by grain size.