Abstract: To explore the effect of biochar on crop nitrogen absorption and atilization under alternate partial root-zone irrigation, the effects of ¹⁵N labelled nitrogen sources with biochar on plant height, stem diameter and dry matter mass and nitrogen absorption by potted tomato organs were evaluated. The experiment set up with three biochar addition levels combined with three nitrogen application levels. The results show that the tomato plant height and stem thickness are greatest at 2% biochar addition and 450 kg/hm~2 N application, and dry matter mass is greatest at 2% biochar addition and 300 kg/hm~2 N application. Both biochar addition and increased N application promote the accumulation of ¹⁵N fertilizer and total N in all tomato organs, and increase ¹⁵N residual and ¹⁵N absorption. Addition of biochar can reduce the nitrogen derived from fertilizer. However it significantly increases soil N absorption, ¹⁵N recovery rate and ¹⁵N utilization rate. Addition of biochar can effectively improve the yield of tomato, water use efficiency and quality of tomato. Among them, the B2N2 treatment has the highest yield of 2.61 kg/plant and the quality has effectively improve, compared with other treatments. The results of the TOPSIS method based on combination weighting is used to evaluate the overall efficiency of tomatoes. The result show that the treatment with 2% biochar addition and 300 kg/hm~2 N application（B2N2） under alternate partial root-zone irrigation is the best planting mode of the conditions of this trial.