Abstract: The Pearl River Diluted Water (PRDW) plays an important role in the physical, chemical and biological characteristics of the northern South China Sea (SCS). Based on the hindcast simulations of the FVCOM (Finite Volume Community Ocean Model) from 1993 to 2012, defining the area enclosed by the sea surface salinity contour of 32 and the coastline as the spreading area of PRDW, the interannual variation of the PRDW spreading area in summer (June, July and August), defined with the area enclosed by the sea surface salinity contour of 32 and the coastline, were studied, and the impacts of the SCS monsoon and the Pearl River discharge on the PRDW were analyzed. Under the influence of prevailing southwesterly winds and strong river discharge, the PRDW can spread to both the west and the east coastal areas of Guangdong and has the maximum spreading area in summer. The spreading pattern and area of the PRDW in summer exhibit significant interannual variation. The anomalous easterly wind in 1994 greatly enhanced the westward spread of the PRDW. Based on the analysis of typhoon “Fengshen” in 2008, it is found that the surface convection and vertical mixing caused by the tropical cyclone had significant influence on the PRDW, but its effects on interannual variation was not obvious due to its short duration. The strong El Niño event in the summer of 1998 led to southwesterly wind anomalies in June, July and August, and the strong southwestly winds supressed the westward spread of the PRDW and enhanced the regional upwelling and surface currents.