Abstract <p>To study the evolution rule of groundwater chemical composition, this paper conducted field geological surveys and sampled water along the groundwater flow direction from northwest to southeast at sampling points W1 to W9. This paper analyzes the hydrochemical types, major ion components, conducts PHREEQC simulation, and investigates ion ratio coefficients of these groundwater samples. The results show that along the groundwater flow direction, the water chemistry type gradually transitions from the HCO₃-Ca to the HCO₃-Ca·Mg, and finally to the HCO₃·SO₄-Ca. Meanwhile, along the direction of groundwater flow, different minerals have different saturation indices, leading to dissolution and precipitation, and thus changes in water chemistry. During groundwater runoff, the hydrodynamic conditions deteriorate, Ca²⁺, Mg²⁺ and Na⁺ undergo ion exchange, while sulphate and carbonate undergo ion exchange and dissolution. In addition, there is a certain linear relationship between Sr and Ca²⁺, and the Na⁺/Cl^– ratio indicates that mineral dissolution occurs during groundwater runoff. In summary, changes in water chemistry occur along groundwater flow due to the influence of the water-bearing medium.</p>