Abstract: High concentration of nitrogen is one of the important factors affecting the river water environment. This paper aims to gain an in-depth understanding of the spatiotemporal variation characteristics of TN concentration in the Luan River Basin. Based on the TN concentration monitoring data in the Luan River Basin during 2018 and 2022, this paper applied spatial cluster analysis, divided the basin into source, upstream and downstream areas, and conducted research on the spatiotemporal distribution characteristics and variation of TN concentration. The influencing factors of TN concentration changes were explained by exploring the relationship between TN concentration and precipitation, runoff and groundwater depth. The results showed that: (1) TN concentration in the source area remained at about 1.86 mg/L, with a relatively low level. The TN nitrogen concentration in the upstream area was highest, with the highest concentration exceeding 10 mg/L, which is closely related to the population concentration, livestock and poultry farming, and agricultural surface pollution in the area. The downstream was regulated by the Panjiakou-Daheiting Reservoir, and the TN concentration was stable at about 5 mg/L. (2) The TN concentration in Luan River Basin was significantly affected by precipitation. When the monthly precipitation was less than 250 mm, TN concentration was strongly negatively correlated with precipitation, showing a decreasing trend of TN concentration as precipitation increased. When the monthly precipitation was greater than 250 mm, the nitrogen in the soil was washed and released, and the TN concentration increased with the increase in precipitation. (3) The regulatory role of the Panjiakou-Daheiting Reservoir significantly affected the reservoir downstream TN concentration. Large releases from reservoirs greatly increased river runoff, which causes the release of nitrogen from the sediment and increases the river TN concentration. (4) The hilly areas of the Luan River Basin has large undulations and shallow groundwater depth, and surface water was recharged laterally by groundwater during dry periods. This resulted in an increase in surface water NO₃⁻-N concentration and led to an increase in TN concentration. The study indicated that the TN concentration in the Luan River Basin showed the trend of upstream > downstream > source area trend. The precipitation and the regulation of the reservoir had a significant effect on TN concentration. Groundwater recharge of surface water during dry periods in hilly areas is one of the reasons for the increase in TN concentration.