Abstract: Submarine groundwater discharge（SGD） is an important process of landocean interaction in coastal zones and adjacent sea areas.It serves as a pathway for terrestrial substance,especially land-nutrients and pollutants,to the coastal ocean.Generally speaking,the groundwater discharge can be estimated by:（1） hydrological calculation;（2） direct measurement;（3） geochemical tracing.In the present paper,the geochemical tracing of radium isotopes for the estimation of groundwater discharge is mainly discussed.By using this method,the data of radium isotope in the northeast coast of Hainan are examined and the corresponding groundwater discharge flux is estimated 0.015dm3(d·cm2).