Abstract: With the processes of ancient sea transgressions, a large amount of salt water has been stored in the subsurface of the Pearl River estuary due to its low hydraulic conductivities in the coastal alluvial plain area.In this paper, we analyze the spatial variation and the source of groundwater salinity, and discuss the process of groundwater circulation in the Pearl River estuary area, using geophysical prospecting technology, total dissolved solid (TDS) and ¹⁴C data.The results of geophysical prospecting show that the groundwater salinity decreases from the east and the west of riverside to the inland, and gradually increase from the north to the south of seaside.The salt water is distributed around 75% of the study area where TDS exceeds 1g/L.The groundwater flow field could be divided into two subsystems.The groundwater flow system in the north is desalinated by receiving surface freshwater and shallow groundwater recharge, while the system in the south is affected by the seawater intrusion and the hydraulic exchange of the subsurface salt water is poor.