A cruise was conducted from 28 July to 21 August 2012 in the northern South China Sea. 31 hydrochemical stations were investigated and 61 samples were collected totally. The salinity and temperature were measured by a temperature and salinity analyzer. Short-lived radium isotopes were measured by a Radium Delayed Coincidence Counter and long-lived radium isotopes were measured by a Canberra germanium well-type gamma detector. The study was to investigate the submarine groundwater discharge flux on the northern South China Sea. In the same cruise, 9 transects were investigated. The temperature and salinity were measured by a Seabird SBE 911 or 917 conductivity-temperature-depth recorder. The temperature and salinity were used to analyze the hydrological characteristics in the northern South China Sea.