Application of nitrogen (N) fertilizer is one of the most important measures to increase grain yield and protein content in winter wheat (Triticum aestivum L.) production.However,misuse of N fertilizer will not only affect grain yield and quality,but also cause the decline of economic benefits and related negative environmental effects.It is essential to study reasonable N application regimes for profitable yields,efficient N utilization and reduction in possible environmental pollution.The objective of this study was to determine the N uptake and translocation in wheat plants by using 15N isotope tracers in PVC cylinders (2.05 m long,0.2 m,without bottom) in seven treatments:without N fertilizer application (NO);N application rate of 168 kg/hm2(0.527 g/pot),with ratios of base fertilizer to topdressing of 1:1 (N1),1:2 (N2) and 0:1 (N3);N application rate of 240 kg/hm2 (0.753 g/pot),with ratios of base fertilizer to topdressing of 1:1 (N4),1:2 (N5) and 0:1 (N6),The 15N tracer experiment showed that the main basal N absorbed by plant from sowing to jointing stage accounted for 78.04%-89.67%;fertilizer N use efficiency (FNUE,N fertilizer accumulation in plant/N supplied) of topdressing was significantly higherthan that of basal N;reducing basal N amount and increasing topdressing N amount could appropriately promote the plant’s absorption of more N fertilizer and enhance FNUE,of which treatment N2 had the highest values.Under the high-yield condition,when N fertilizer rate was increased from 168 to 240 kg/hm2,there were no significant differences in the amount of N accumulation in plants and in grains between treatments with the same ratio of base fertilizer to topdressing;by reducing basal N amount and increasing topdressing N amount accordingly,the translocation efficiency (TE,accumulation amount from vegetative organs to grain/N accumulation in vegetative organs during anthesis) increased,and the amount of N assimilation to grains after anthesis and its contribution proportion (the amount of N assimilation to grains after anthesis/N accumulation in grain) also increased.In other words,grain N accumulation amount increased with increasing amount of topdressing N at the same N fertilizer rate.There were no significant differences among treatments N2,N3,N5 and N6 in grain N accumulation.Appropriate N fertilizer rate with a reduction in basal N amount and an increase in topdressing N amount such as in N2,N5 and N6 increased grain yield and protein content.In conclusion,under conditions used in this experiment,as far as grain yield,protein content and FNUE are conced,the recommended appropriate N fertilizer application regime is treatment N2,with a N fertilizer rate of 168 kg/hm2 and a ratio of base fertilizer to topdressing of 1:2.