Abstract: Due to long-term over-exploitation of groundwater, the groundwater level in the Hutuo River alluvial plain continued to decline, and the water quality deteriorated. In order to alleviate the contradiction of water resources in this area, a river replenishment project was implemented in 2018. The water source for replenishment was contributed by Huangbizhuang Reservoir and the water originated from the 'South-to-North Water Diversion Project'. In order to study the changes in groundwater chemistry after replenishment, on-site monitoring and groundwater chemical testing were carried out, and further joint analysis was carried out through hydrogeochemistry, hydrology, statistics and other theoretical methods. The results showed that: (1) After the Hutuo River water replenishment was implemented, the groundwater level increased significantly. The average groundwater level along the Hutuo River rose by 5.83 m. Regionally, compared with 2015, the groundwater level in 2019 increased by an average of 5.93 m. The shape of the groundwater funnel also changed, and it no longer clearly showed that the groundwater converged towards the center of the funnel. (2) Affected by the long-term supply of high sulfate brine sources in the upper stream of the Hutuo River, the groundwater along the watercourse was dominated by the water type of HCO₃·SO₄-Ca·Mg, and strip-shaped HCO₃·SO₄·Cl-Ca·Mg water was distributed further along both sides. However, compared with year of 2015, HCO₃-Ca·Mg water area decreased by 20.6% in 2019, while HCO₃·SO₄·Cl-Ca·Mg water and HCO₃·SO₄-Ca·Mg water increased by 13.6%. (3) The river replenishment effectively alleviated the deterioration of the groundwater environment. The regional groundwater sulfate level remained relatively constant, while the chloride, TDS, and total hardness showed a downward trend. Affected by the water replenishment of Huangbizhuang reservoir, high-concentration sulfates are mainly distributed near the Hutuo River, Shijin Irrigation Canal and the auxiliary dam of Huangbizhuang Reservoir. With the continuous advancement of water replenishment, the water level continued to rise, and under the action of hydrodynamics, there was a tendency to diffuse downstream. The studies have shown that scientifically and rationally selecting water replenishment sources and replenishment methods is an effective way to mitigate the sulfate pollution of groundwater in this area and maintain the sustainable use of groundwater.