Abstract: Understanding the chemical characteristics of groundwater and its formation has great significance for identifying water inrush source rapidly and preventing water inrush. Quadratic fitting curve of each conventional ion and TDS(total dissolved solids), ion concentration coefficient of variation piper trilinear nomograph, groundwater Stiff diagrams, TDS contour map, Gibbs diagram and ion ratio coefficient map were used to analyze groundwater chemical characteristic of each aquifer and its formation on the basis of systematic analysis of hydrogeological conditions in Fengyu mine. The analysis results indicate that ion concentration coefficient of variation of each aquifer was less than1, and the distribution of ions was relatively stable; hydrochemistry type of Shanxi Formation and Taiyuan Formation was HCO₃·Cl-Na+K·Ca, and the concentration of Na⁺+K⁺ and TDS was greater than others, which means that Shanxi Formation and Taiyuan Formation were relatively closed aquifers; the water chemistry type of Cenozoic and Ordovician was HCO₃-Ca·Mg; the main factors influencing the chemical components of each aquifer were water-rock interaction, including carbonate dissolution, silicon aluminate solution, evaporite solution.