Abstract: Field experiments were conducted to study effects of nitrogen application rate and ratio of base and topdressing on nitrogen utilization,grain yield, and grain protein content in winter wheat using 15N tracer technique. Results showed that using nitrogen increased nitrogen cumulate,grain yield,protein content,and grain protein yield.Under the same nitrogen application rate,higher topdressing ratio improved nitrogen agronomic efficiency,nitrogen recovery efficiency,increased accumulation amount of topdressing fertilizer nitrogen and soil nitrogen in above-ground part(nutrition part + kernel),and improved transferring amount from nutrition part to kernel,assimilating amount after anthesis,and protein content.Under the same ratio of base and topdressing,decreasing nitrogen application rate from 240 kg/ha to 168 kg/ha increased nitrogen agronomic efficiency,nitrogen recovery efficiency,and nitrogen partial factor productivity,meanwhile,accumulation amount of soil nitrogen in kernel,accumulation amount of soil nitrogen in above-ground part,and assimilating amount after anthesis and protein content were improved as well.Grain yields had no statistical significant difference among different nitrogen application treatments.Under the field fertility of this experiment,one time application of 168 kg/ha nitrogen at jointing stage,was the optimal treatment taking account of yield,quality,and benefit.