To explore the yield?increasing effect and physiological mechanism of boron (B)?nitrogen (N) interaction in Brassica napus, the effects of B?N different treatments on rapeseed growth, N uptake and utilization, N metabolism enzyme activity, and seed yield were analyzed by hydroponic culture experiment and field plot experiment. The results showed that B deficiency significantly inhibited the root growth of rapeseed at the seedling stage under different N supply levels. Compared with low N or low B treatment, the balanced supply of B and N significantly increased the N uptake and the expression level of related genes, and improved the activities of nitrate reductase (NR) and glutamine synthetase (GS) in N metabolism. In the field experiment, the application of B and N fertilizer significantly increased the seed yield of rapeseed. However, the effect of B fertilizer application was closely related to soil N availability. Under the normal N supply level(180 kg/hm²), the effect of B fertilizer application was better than that of low N (60 kg/hm²) condition, while high B (18 kg/hm²) combined with high N (240 kg/hm²) limited the further increase of seed yield. Appropriate co?application of B and N significantly improved the N harvest index and promoted the distribution of N to the grains. B and N co?application had significant interaction effects on the growth and development of rapeseed, both in the hydroponic seedling stage and in the field of the whole growth stage. Under the field conditions of this study, the recommended amount of N fertilizer was 180?240 kg/hm², and the combined application with 4.5?9 kg/hm² of borax could maximize the yield increasing potential of rapeseed.