Abstract: Grain-size analysis was carried out for the sediments taken from the upper part of the Core SYS-0803 drilled in the western South Yellow Sea. The components sensitive to depositional environment are carefully studied. The vertical variation in sediment grain size, in combination with the reflection characteristic of seismic profiles, suggests that the sediment grain-size parameters may effectively indicate the paleo-environment evolution. The study area has passed through a sequence of environmental changes from coastal-shallow water to fluvial deposition, to estuary deposition and to coastal-shallow water, and ended in an environment of continental shelf in an ascending order.