Abstract: The groundwater recharge by the South-to-North Water Transfer Project in Chaobai River is a strong guarantee for the sustainable supply of groundwater sources and the ecological restoration of the rivers in the Miyun-Huairou-Shunyi (Mi-Huai-Shun). Based on the long-term water quality monitoring data in the recharge area, water quality evaluation, hydrogeochemical simulation, and statistical methods were used to analyze the characteristics of the groundwater hydrochemical changes. Meanwhile, the hydrogeochemical simulation software (PHREEQC) was used to simulate the hydrogeochemical changes near the rivers affected by the core water transfer route, the Xiaozhong River. Combined with the cluster analysis method, the influencing factors of hydrogeochemical changes were elucidated. The results showed that both the surface water quality and groundwater quality in the recharge area were good, the main chemical types of the water of South-to-North water diversion and local groundwater were HCO₃-Ca-Mg. It also showed that the groundwater quality had been improved because of the recharge. The concentrations of Na⁺ and Cl⁻ in the groundwater of the recharge area decreased significantly. The hydrogeochemical simulation indicated that after receiving the South-to-North water recharge, the proportion of the South-to-North water in the groundwater near the main recharge river was about 10% by the end of 2017. Furthermore, the groundwater near the river was dominated by South-to-North water after the recharge in 2018 and 2019, and the chemical compositions of groundwater were basically the same as those of South-to-North water. According to the simulation of water-rock interaction, the main factors affecting the groundwater quality in the recharge area included mixing of the south water and with local groundwater, mineral dissolution, and cation exchange. These findings can provide a scientific basis for site selection, planning, and water source selection for the safe natural infiltration of rivers to replenish groundwater.