Abstract: 198 samples of surface sediments collected from the northwestern South China Sea were analyzed for major elements, in order to investigate their distribution pattern, enrichment mechanism and grain size effect. The sediments in the study area have relatively high contents of SiO₂,Al₂O₃ and CaO, 45.9%,8.53% and 16.7% respectively on average. The SiO₂ and Al₂O₃ abundance represents detrital materials, and CaO abundance is an indicator of the bioclast component. The samples taken from the continental slope are usually high in SiO₂ compared to those from continental shelf, but low in Al₂O₃ and CaO. The distribution patterns of Fe₂O₃,K₂O,MgO,Na₂O and TiO₂ are similar to that of Al₂O₃, indicating that they are absorbed by fine-grained clay minerals. The correlation indicates that the dilution effect caused by quartze and carbonate also can be founded. The enrichment index for most of the major elements ranges from 1 to 2, suggesting that they mainly derived from the continental crust. However, the relatively high abundance of CaO、MnO may indicate the significant contribution of biogenesis and chemical process on the continental slope.