Binhai County, Jiangsu Province, is rich in groundwater resources, and the deep groundwater is one of the most important sources of water supply for local residents, living and production. In order to investigate the hydrochemical characteristics and control factors of the deep groundwater in Binhai County，Northern Jiangsu Province，and to safeguard the development and water supply security of groundwater resources.Methods:The study collected a total of 43 samples of deep groundwater (the Ⅱ, Ⅲ and Ⅳ pressurized aquifers)andseawater. Combined with the hydrogeological conditions and current situation of groundwater exploitation,statistical analysis, Piper trilinear diagram, Gibbs diagram, Schoeller diagram, ion correlation analysis and ion ratio and other methods were used to analyze the chemical composition of groundwater and spatial distribution characteristics and to investigate the controlling role and formation mechanisms of the hydrochemical components of deep groundwate.Results: ① the deep groundwater within the Binhai County region is typocally moderately alkaline, with notable variations in Total dissolved solids（TDS） levels across different aquifers. This variations tend to increase from west to east (from land to sea). ② The hydrochemical characteristics of groundwater have the obvious zonation patterns.The main hydrochemical types of the secong confined groundwater are Cl-·HCO-3—Na+ and HCO-3—Na+ types; the main hydrochemical types of the third confined groundwater are Cl-·HCO-3—Na+ and HCO-3·Cl-—Na+ types; the hydrochemical types of the fourth confined groundwater is Cl-·HCO-3—Na+ type. With the increase of depth, hydrochemical types have changed from pluralism to singleness. ③ The hydrochemical characteristics of the study area are affected by water—rock cation exchange, rock weathering and dissolutionare the main controlling factor.Moreover,the cation exchange is active. Ca2+, Mg2+, HCO-3, etc. in deep groundwater mainly come from the dissolution of silicate rock,While, Na+, SO2-4, Cl-, etc. mainly come from the dissolution of evaporite saline rocks and sulfate rock.Conclusions: The current hydrochemical characteristics of deep groundwater have not yet been significantly affected by human activities such as long- term over- exploitation of groundwater. To avoid or slow down risk of deep groundwater salinization and other environmental issues, it is recommended to reasonably distribute deep groundwater extraction wells and reasonably regulate the amount of withdrawals.These results findings have important implications for groundwater sustainable development and environmental protection in such water- receiving areas of the coastal area of Jiangsu Province.