Abstract: Pot culture and field experiments were carried out with one-year-old apple rootstock M9T337 seedlings and five-year-old ‘Yanfu3’/SH6/M. hupehensis Rehd. as test materials respectively. Combined with ¹⁵N and ¹³C isotope tracer technology, we examined the effects of different concentrations of NR inhibitor Na₂WO₄(0, 0.5, 1, 1.5 mmol·L^-1, expressed by CK, T₁, T₂ and T₃ respectively) on ¹⁵N absorption and ¹³C accumulation of seedling and apple quality. The results showed that 0.5-1.0 mmol·L^-1 Na₂WO₄ significantly inhibited shoot growth but not root growth of seedling in the pot experiment. Root growth was significantly inhibited when the concentration of Na₂WO₄ reached 1.5 mmol·L^-1. The NR activity of each treatment was negatively correlated with the concentrations of Na₂WO₄ in the same period, with an order of CK>T₁>T₂>T₃. The content of nitrate in leaves showed the trend of first rising and then decreasing with the extension of processing time. Nitrate content was positively correlated with Na₂WO₄ concentration in the same period, with an order of T₃>T₂>T₁>CK. Spraying Na₂WO₄ reduced the ¹⁵N absorption of each organ and ¹⁵N utilization rate, with such effects increasing with the amount of spraying. With the increases of Na₂WO₄ concentration, ¹³C accumulation on the ground increased first and then decreased, with highest value in T₂ treatment. The ¹³C accumulation of whole plant showed a similar pattern. The results of field experiment showed that Na₂WO₄ application reduced nitrogen contents of leaves and fruits at maturity stage, and increased the anthocyanin content in peel, soluble solids, soluble sugar content and sugar acid ratio in fruits. The T₂ treatment showed the best effect. In summary, T₂ treatment (1.0 mmol·L^-1 Na₂WO₄) could inhibit shoot growth of seedlings, reduce ¹⁵N absorption and utilization, improve ¹³C accumulation, which would improve apple quality.