Abstract: The utilization of reclaimed water to replenish river area may pose environmental risks due to the difference between reclaimed water and groundwater. The water diversion project from the Wenyu River to the Chaobai River has been in operation for more than 10 years. To investigate the evolution characteristics and mechanisms of nitrogen components in groundwater at different locations under long-term river infiltration of reclaimed water, the monitoring data of surface water and groundwater in 11 years were collected. Meanwhile, cluster analysis was conducted to divide the surface water into different regions and typical groundwater monitoring points were selected to reveal the evolution difference of nitrogen components. Cl^- was used to calculate the mixing ratio and get the calculated concentration of the target components in groundwater, which can infer the nitrogen transformation after surface water infiltrating into subsurface. The environmental indicators such as DO, TOC, sediment, and hydrogeological conditions were also used to support the abovementioned results. The results showed that: (1) The surface water could be divided into three groups, including the Jian River, Chaobai River section in the north and that in south of the earth-filled dam. There were significant differences among the indicators of these three groups. The water quality difference was mainly affected by the nitrogen, phosphorous and water flow pattern of reclaimed water. (2) During the infiltration process of reclaimed water, the thicker vadose zone or the clay layer was conducive to nitrogen removal, NO₃^--N in the surface water of the Chaobai River section to the north of earth dam and the Jian River decayed through denitrification and assimilation in vadose zone, and NH₄⁺-N was removed through nitrification and adsorption. The infiltration process did not cause an obvious increase in groundwater nitrogen concentration. (3) However, in the Chaobai River section to the south of the earth-filled dam, the groundwater level rose rapidly and tended to be stable after one year of river water replenishment. The long-term infiltration of surface water increased the content of nitrogen and organic matter in the sediment, which made the section reach a proper carbon-nitrogen ratio after 2013 and led to organic nitrogen mineralization. Due to the thin aeration zone, the generated NH₄⁺-N was less adsorbed in the soil, and consequently, most of NH₄⁺-N would infiltrate into groundwater and result in the increase of ρ(NH₄⁺-N). The results of this study indicated that in the infiltration process of reclaimed water, a thick aeration zone or clay layer could effectively remove nitrogen components. However, in some areas, the aeration zone was thin and organic nitrogen mineralization occurred, which increased the risk of nitrogen pollution of groundwater.