~(234)Th-~(238)U disequilibria were applied to examine the particle dynamics in the euphotic zone of the central South China Sea during the spring 2002 cruise.The particulate organic carbon (POC),~(234)Th (including both dissolved and particulate) and ~(238)U in the water column at three stations were determined. The profiles of ~(234)Th/~(238)U activity ratio at the three stations all showed consistent ~(234)Th deficit as compared to ~(238)U in the upper 100 m water column.Based on the profiles of the dissolved and particulate ~(234)Th and a steady state box model,the dissolved ~(234)Th scavenging rates,the particulate ~(234)Th removal rates and their resident times were quantified.It was found that the POC downward export fluxes out of the upper 100 m euphotic zone ranged from 9.40 to 14.78 mmol·m~(-2)·d~(-1).The results from this study provide new information for our understanding of carbon biogeochemical cycle in the South China Sea. ~ (234) Th ~ (238) U disequilibria were applied to examine the particle dynamics in the euphotic zone of the central South China Sea during the spring 2002 cruise.The particulate organic carbon (POC), ~ (234) Th (234) Th / ~ (238) U activity ratio at the three stations all showed consistent ~ (234) Th deficit (238) U in the upper 100 m water column. Based on the profiles of the dissolved and particulate ~ (234) Th and a steady state box model, the ~ 234 234 Th scavenging rates, the particulate ~ (234) Th removal rates and their resident times were quantified. It was found that the POC downward export fluxes out of the upper 100 m euphotic zone ranged from 9.40 to 14.78 mmol · m -2 (d -1) . The results from this study provide new information for our understanding of carbon biogeochemical cycle in the South China Sea.