Abstract: The groundwater in the northern region of China is an important source for water supplement. In recent years, with the acceleration of urbanization and the impact of human activities, the hydrochemical characteristics of groundwater have become increasingly complex. It is important to identify the hydrochemical characteristics of groundwater in the water source areas and the cause mechanisms for the rational development and utilization of groundwater resources and for the insurance of local socio-economic sustainable development and ecological security. Based on the collection of groundwater samples, the mathematical statistics, correlation analysis, Piper three-line diagram, Gibbs diagram, and the ratio of groundwater main ions were applied to analyze the chemical characteristics and genetic mechanism of the groundwater in Jiuxian County, Tai'an City. The results showed that the chemical types of groundwater in the research area were diverse. The pore water was mainly HCO₃-Ca, HCO₃+SO₄-Ca type, and the karst water was HCO₃-Ca, HCO₃-Ca+Mg, HCO₃+SO₄-Ca, and HCO₃+SO₄-Ca+Mg type. The chemical composition of pore water and karst water in the area was mainly controlled by both of the natural and human factors. The main ionic components of groundwater were affected by the interaction of water and rock. The ions mainly came from the dissolution of carbonate rock, calcite, and dolomite, and the cation exchange effect was weak. Moreover, the increase of the concentration of Cl⁻ and NO₃ ⁻ in groundwater was due to human activities.