Abstract: The Southern Yellow Sea is an important passage for transporting terrigenous materials from the East Asian continent to the western Pacific Ocean. It is of great significance to clarify the size and distribution patterns of the particles transported through the Southern Yellow Sea for further understanding the source to sink system of the region. In this paper, we analyzed the grain size distribution and its influencing factors based on the hydrological and LISST data measured in the Southern Yellow Sea during the summer season of 2012. The results show that fine particles (≤128 μm) are mainly composed of inorganic particles, while the coarse (＞128 μm) dominated by organic particles during the summer season. The inorganic particles are mainly distributed in the well-mixed coastal shallow area and the bottom layer offshore, while organic particles mainly occupy the pycnocline where the water is highly stratified. The resuspended surface sediment is the main source of inorganic particles, and the tidal mixing process is the main driving force of resuspension. The tidal mixing front prevents the coastal inorganic particles from spreading to the offshore area in bottom layer, but some finer particles (＜16 μm) can be transported to the central Southern Yellow Sea by surface cross-front currents. The pycnocline obstructs the upward diffusion of nutrients inside the Yellow Sea Cold Water Mass, which leads to the accumulation of phytoplankton in the pycnocline. The coarse particles (＞128 μm) are mainly from the plankton or aggregates formed by organic secretion mixed with fine inorganic particles. The formation of aggregates enhances the sedimentation of surface fine inorganic particles and promotes the formation of mud deposits.