[Objective] To explore how biochar（ BC） addition affects the change of soil nitrogen（N） under high N deposition. [Methods] Taking the loess plateau abandoned grassland as the research object, we set up the control（N0BC0）, high N（N9BC0）, BC addition（N0BC20） and its composite treatment（N9BC20） to analyze the change rule of different treatments on the soil nitrogen component and the spatial distribution characteristics. [Result] 1) Compared with the control, N9 BC20 treatment significantly increased the contents of TN, NH₄⁺-N and DON by 1.95, 1.70 and 1.44 times, respectively. Compared with N9BC0 treatment, N9BC20 treatment significantly increased soil TN, DON, and DTN contents in the 0-40 cm soil layer by 1.39, 1.35 and 1.22 times, respectively. Soil NH₄⁺-N, NO₃^--N and MBN contents under different treatments decreased with the increase of soil depth. 2) N9BC0 treatment decreased soil DON/DTN ratio in the 0-40 cm soil layer. However, the N9BC20 treatment increased soil NO₃^--N/DTN and DON/DTN ratios in the 0-40 cm soil layer, and promoted the conversion of soil NH₄⁺-N to NO₃^--N. 3) The NPMIs of NH₄⁺-N, DTN, and DON in the 0-40 cm soil layer under the N9BC20 treatment were all the largest, being 1.08, 1.36 and 1.60 times of that of N9BC0 treatment, respectively. 4) Regression analysis showed that soil bulk density explained 22.6% of the variation in TN, and soil total phosphorus and pH together explained 53.7% of the variation in TN. [Conclusion] BC addition can regulate the dynamics of soil N pools by altering abiotic factors in soils on the Loess Plateau and can be a potential measure for N fixation and soil fertility enhancement for soils on the Loess Plateau under the background of high N deposition in the future.