In order to explore the effects of the combination of biochar and nitrogen fertilizer on the circulation of soil nitrogen and nitrogen utilization in flue-cured tobacco, a pot experiment was conducted with ¹⁵N trace technique. Four treatments were set: 5 g pure nitrogen per pot (CK), 5 g pure nitrogen and 100 g biochar per pot (T1), 3.5 g pure nitrogen and 100 g biochar per pot (T2), 2 g pure nitrogen and 100 g biochar per pot (T3). The contents of ¹⁵N, NH₄⁺-N, NO₃^--N, alkali hydrolysable nitrogen(AN) and microbial biomass nitrogen (MBN) in soil in different growth periods and the accumulation of nitrogen from different resources in leaves at 90 days after transplanting were measured. The results showed under the same content of nitrogen, biochar application improved the contents of ¹⁵N, NH₄⁺-N, NO₃^--N, AN and MBN in soil and the nitrogen accumulation in tobacco leaves. The combination of biochar and nitrogen fertilizer improved the percentage of nitrogen fertilizer in leaves and increased the rate of ¹⁵N utilization by 25.4%–63.6%. Compared with CK, the contents of NH₄⁺-N, NO₃^--N, AN and SMBN of T2 increased 17.3%, 8.0%, 7.2% and 11.3%, respectively at 75 days after transplanting, AN and SMBN were also higher than the control at 90 days. Under the test conditions, the combination of biochar and nitrogen fertilizer has a significant effect on soil nitrogen, and the reduction of nitrogen fertilizer by 30% is feasible when biochar applied.