This paper reviews the current research status and main open problems of four hot topics in the study of coastal hydrogeology. The review includes the following aspects: ① analytical studies of the tideinduced groundwater level fluctuations in coastal aquifers and their applications, ② the study of the interactions of seawater and groundwater in the intertidal zone and its applications to the remediation of oil spilled beaches, ③the study of the subsurface airwater twophase flow induced by tides and rainfall in coastal areas and their engineering and ecological impacts, and ④quantitative estimation of the Submarine Groundwater Discharge (SGD).