The Taizhou urban area is located at the junction of the hydrogeological subzones of the northern Yangtze River Delta Plain and the Lixiahe Low-lying Lake-dotted Plain. To compare and study the hydrochemical characteristics of the phreatic layer in the two sub regions, the spatial distribution, hydrochemical types, correlation relationships, and ion sources of the main hydrochemical indicators were analyzed through methods such as charge balance, statistical analysis, Piper plot, Gibbs plot, ion ratio, and correlation analysis. The causes of hydrochemical evolution and the sources of differences between the two sub regions were explored. The results show that the content of cations in the phreatic water in the area is Ca²⁺ > Na⁺ > Mg²⁺ > K⁺, and the content of anions is HCO_3- > > Cl ^-. The northern part is mostly brackish water, and the central and southern parts are mainly fresh water.The content of main indicators gradually decreases from north to south. The hydrochemical characteristics are mainly silicate weathering water rock interaction. The remaining components of the Holocene transgression have only a small impact on the northern phreatic water. The impact of human activities is mainly agricultural irrigation, Cation Exchange interaction occurs in the form of positive cation exchange. There are obvious differences in hydrochemical composition and hydrochemical types between the two sub regions. The main causes of the differences in hydrochemical characteristics between the two sub regions are the different sedimentary environments and geomorphological effects after the Holocene sea retreat.