Abstract:  In order to study the chemical characteristics and formation of groundwater in Cenozoic basalt in North China，the groundwater  of the basaltic aquifer of Zhangbei County was taken as the research object. Based on the field collection of groundwater samples and the determination of groundwater chemistry and isotopic composition, the hydrochemical formation mechanism of basalt groundwater in the study area was analyzed by means of statistical analysis, ion proportion coefficient, hydrogen and oxygen isotopes, and inverse geochemical simulation. The results show that along the direction of groundwater flow, most of the ions in basalt groundwater are increasing. The chemical types of groundwater in the recharge area are mainly HCO3Ca·Mg, with the average TDS less than 500 mg/L, while the anions in groundwater in the discharge area are mainly Cl-, cations are mainly Na+, and the average TDS is more than 1 400 mg/L; The groundwater recharge in the study area is the local atmospheric precipitation and the weathering and dissolution of aluminosilicate, and rock salt and sulfate are the main sources of ions in groundwater; The effects of human activities such as dissolution and filtration, cation alternate adsorption, and agricultural fertilization are the main factors controlling the hydrochemistry of groundwater.

Key words: groundwater, hydrochemistry, stable isotopes, basalts, Zhangbei County, Hebei Province