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 tide-induced 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; 3) the study of the subsurface air-water two-phase flow induced by tides and rainfall in coastal areas and their engineering and ecological impacts; and 4) quantitative estimation of the Submarine Groundwater Discharge(SGD).