Clayey aquitard porewater reserves the information of hydrological environment in the formation and evolution process of groundwater to a large extent. In order to investigate the salinization process of shallow aquitard porewater in coastal zones, aquitard porewater was extracted from two boreholes, namely H1 and H2, in north Jiangsu coastal zone with a depth of 0-35m. The analysis of porewater indicates that the TDS (total dissolved solids) concentrations of H1 borehole and H2 borehole, 7 km apart, ranged from 3.6 to 9.9 g/L and 12.5 to 37.0 g/L, respectively. Br- was obviously enriched compared with the regional fresh groundwater, and the concentration of Na+ and Ca2+ ranged differently compared with the seawater composition. Aquitard porewater had the most enriched isotopic values at the depth of 10.1 m, which decreased toward both ends and obviously gathered below the intersection of local meteoric water line (LMWL) and mixing line between seawater and groundwater. The δD-δ18O relationship and the Cl-Br relationship indicate that porewater could be originated from Holocene seawater and was subsequently diluted with modern meteoric water, whereas porewater of H2 borehole located in salt field was affected by brine mixture. Enrichment or depletion of Na+ and Ca2+ indicate that water-rock interaction also accounted for the salinization of shallow aquitard porewater.