Based on the water diversion project from Wenyu River to Chaobai River, the leaching experiment was carried out to study the cation exchange adsorption mechanism and TN and NO^-₃-N removal effect of riverbed medium in the process of the reclaimed water passing through riverbed. According to the groundwater quality monitoring data, the interaction mechanism of water and rocks between the reclaimed water and riverbed medium was verified. The results show that the salinity in groundwater increases for nine years of using the reclaimed water. Though the infiltration of reclaimed water causes the exchange between K⁺ in water and Ca²⁺ in soil, the total hardness of groundwater decreases. The concentration of NO^-₃-N is very low in groundwater due to the significant removal effect of riverbed medium. For inorganic components, the reclaimed water has no negative effect.