Abstract: Based on major and trace element data from 142 surface sediment samples collected from the southwestern waters off Cheju Island off Korean Peninsula in the southwest, the chemical composition, sediment sources, and controlling factors were revealed systematically through cluster analysis, factor analysis, and geochemical discrimination diagrams. Results show that the study area could be divided into three geochemical provinces as revealed by cluster analysis. Province I is a fine-grained muddy area in which major elements (Based on major and trace element data from 142 surface sediment samples collected from the southwestern waters off Cheju Island, this study systematically reveals the compositional characteristics, sediment sources, and controlling factors through cluster analysis, factor analysis, and geochemical discrimination diagrams. Cluster analysis divides the study area into three geochemical provinces. Province I is a fine-grained muddy area, significantly enriched in major elements such as Al₂O₃, TFe₂O₃, TiO₂, MgO, MnO, and trace elements including Cu, Pb, Zn, Cr, Ni, Co, Li, Rb, V, Sc, Cl, and S. Province II is dominated by coarse-grained siliciclastic sediments with high contents of heavy minerals enriched in elements such as Zr and Hf, indicating a high-energy hydrodynamic sorting environment. Province III exhibits significant enrichment of CaO and Sr, reflecting the dilution of terrigenous detritus by carbonate. Factor analysis indicates that sediment composition is primarily controlled by terrigenous input, superimposed by the combined effects of human activities, biogeochemical processes, and hydrodynamic sorting. Provenance tracing based on discrimination diagrams of CIA-Al/Na, Rb/Sr-K/Na, and A-CN-K reveals significant differences among the provinces. Province I is influenced by a cyclonic eddy jointly driven by the Yellow Sea Warm Current and the Yellow Sea Coastal Current, mainly accumulating mixed fine-grained sediments derived from the Yellow River and the Yangtze River. Province II is mainly distributed in the Yangtze Shoal and the East China Sea shelf sand ridge areas, with sediments derived predominantly from the Yangtze River and subjected to strong hydrodynamic reworking. Province III exhibits a mixed signature of Yellow River materials and carbonate-rich sediments carried by the Yellow Sea Warm Current. This study systematically elucidates the spatial distribution and major controlling factors of sediment geochemical characteristics in the southwestern Cheju Island muddy area and its surrounding waters, providing a geochemical basis for a deeper understanding of the “source-to-sink” processes and sedimentary environmental changes in the northern East China Sea shelf. MgO, MnO) and trace elements (Cu, Pb, Zn, Cr, Ni, Co, Li, Rb, V, Sc, Cl, and S) were enriched significantly. Province II is dominated by coarse-grained siliciclastic sediments enriched in heavy mineral elements (Zr and Hf), indicating a high-energy hydrodynamic sorting environment. Province III exhibits significant enrichment of CaO and Sr, reflecting the dilution of terrigenous detritus by carbonate. Factor analysis indicated that sediment composition is controlled by terrigenous input, superimposed by the effects of human activities, biogeochemical processes, and hydrodynamic sorting. Provenance tracing based on discrimination diagrams of CIA-Al/Na, Rb/Sr-K/Na, and A-CN-K revealed significant differences among the provinces. Province I is influenced by a cyclonic eddy jointly driven by the Yellow Sea Warm Current and the Yellow Sea Coastal Current, accumulating mainly the mixed fine-grained sediments derived from the Yellow River and the Yangtze River. Province II is mainly distributed in the Yangtze Shoal and the East China Sea shelf sand ridge areas, where sediments are derived predominantly from the Yangtze River and subjected to strong hydrodynamic reworking. Province III exhibits a mixed signature of Yellow River materials and carbonate-rich sediments carried by the Yellow Sea Warm Current. This study systematically elucidated the spatial distribution and major controlling factors of sediment geochemical characteristics in the southwestern Cheju Island muddy area and its surrounding waters, provided a geochemical basis for a deeper understanding of the “source-to-sink” processes and sedimentary environmental changes in the northern East China Sea shelf.