The coastal plain of Jiangsu Province is a fragile zone of water resources in Jiangsu Province, and groundwater salinization has become a serious ecological problem. In order to analyze the groundwater recharge and its salinity sources in the north flank of the Changjiang River Delta since Pleistocene, a 275 m deep well HYRD1 was deployed and the whole hole was continuously collected with easily soluble salt samples, geotechnical samples and water samples. Surface water, shallow and deep groundwater, and seawater samples were collected in the area. The hydrochemical characteristics of Well HYRD1 high-precision porewater were obtained by using soluble salt index combined with geotechnical index (water content, wet density, specific gravity). In order to analyze the groundwater recharge and its salt source since Pleistocene, Piper trilinear diagram, Gibbs diagram and ion ratio method were used in combination with δD and δ¹⁸O data and ¹⁴C data. The results show that the salinity of Well HYRD1 soil is mainly NaCl, and the percentage of saline soil is 25%. The saline soils are mainly distributed in the Q_p3 aquitard, Q_p2 stratum and the upper part of Q_p1 stratum. The water chemistry type of porewater is Cl-Na type (only the lower section of Q_p1 is HCO$_3^- $-Ca·Na at individual points), 7% of brackish water, 49% of saline water and 44% of haline water. The brackish water is mainly distributed in the sand layer of the lower section of Q_p1. The δ¹⁸O and δD of diving indicate that the source of diving is atmospheric precipitation and is subject to a relatively strong evaporation effect. The δ¹⁸O and δD of the aquitard pore water and pressurized water are located near the standard seawater dilution line, and the trend of δ¹⁸O and δD decreases with the increase of depth, which indicates that the porewater is subjected to the mixing effect of seawater decreases with the increase of depth. Calcareous nodules are mostly seen in the Q_p1 aquitard, indicating that the Q_p1 aquitard was subjected to strong evaporation after soil formation. The salinity of the upper part of Well HYRD1 Q_p1 and the overlying strata is mainly from the 5th stage sea erosion, evaporite and silicate weathering dissolution. The salinity of the lower part of Q_p1 is mainly from the crustal source. The groundwater chemistry is influenced by water-rock action, evaporation concentration and human activities.