Abstract:The groundwater resources in Binhai County, Jiangsu Province, is rich, the groundwater in deep aquifer system is one of the most important source of water supply for local residents living and production.In order to safeguard the development, protection and water supply security of groundwater resources, the study collected various groundwater 43 samples form regional deep groundwater (the Ⅱ, Ⅲ and Ⅳ pressurized aquifers)and 1 seawater sample.Base on comprehensive the hydrogeological conditions and the status quo of groundwater exploitation,this paper used statistical analysis, Piper trilinear diagram, Gibbs diagram, Schoeller diagram, ion correlation analysis and ion ratio and other methods to study the chemical composition of groundwater and spatial distribution characteristics and water chemistry types of deep groundwater in the study area,the formation mechanisms and control of water chemistry were discussed.The results show that the deep groundwater is moderately alkaline in general, and the total dissolved solids (TDS) is less than 1g/L in the study area, different types of groundwater showed significant spatial variations,gradually increasing tred from west to east (from land to sea). The results show that the types of water chemisty have horizontal distribution characteristics.The main hydrochemical types of the secong confined groundwater are Cl?HCO3-Na and HCO3-Na types; the main hydrochemical types of the third confined groundwater are Cl?HCO3-Na and HCO3?Cl-Na types; the hydrochemical types of the fourth confined groundwater is Cl?HCO3-Na type. With the increase of depth, hydrochemical types have changed from pluralism to singleness. 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+, HCO3-, etc. in deep groundwater mainly come from the dissolution of silicate rock,While, Na+, SO42-, Cl-, etc. mainly come from the dissolution of evaporite saline rocks and sulfate rock.The current hydrochemical characteristics of deep groundwater have not been significantly affected by human activities such as long-term over-exploitation of groundwater. To reduce the risk of deep groundwater salinization and other environmental issues, deep groundwater exploitation wells should be carefully positioned and regulaterd. These findings have important implications for groundwater sustainable development and environmental protection in such water-receiving areas of the coastal area of Jiangsu Province.