Abstract: Dissolved organic carbon (DOC) concentrationin the Pearl River Estuary in summer was observed by high temperature combustion method, the result showed that a great difference of the DOC concentration among the different sources freshwater bodies in the upper reaches of Humen outlet.While the highest DOC (479 μmol/L) was observed in Guangzhou section, it decreased drastically in a 70 km voyage from Guangzhou to Humen outlet.Three tributaries of the Dongjiang River flow into the main stream, bringing an average 227 μmol/L DOC concentration freshwater, the remittance of the relatively low DOC in Dongjiang River and the removal effect of DOC reduced the DOC in the main stream, DOC was only 139 μmol/L in Humen outlet, i.e., the concentration of DOC decreased totally 340 μmol/L in the main stream from Guangzhou to Humen outlet.A three-component model was used to discuss the respective contribution of removal and dilution effects, the running results showed that the removal and dilution effects were 228 μmol/L (accounting for 67%) and 112 μmol/L (accounting for 33%), respectively, the removal effect was the dominant process while the dilution effect can not be neglected.