This study was aimed to explore the optimal water and nitrogen allocation of winter wheat and achieve the efficient utilization of nutrient and water resources. Three irrigation supply levels (low, 25 mm, W1; moderate, 40 mm, W2; high, 55 mm, W3) and five nitrogen supply levels (N0, 0 kg/hm²; N1, 80 kg/hm²; N2, 180 kg/hm², N3, 240 kg/hm², N4, 300 kg/hm²) were designed to optimize the crop irrigation and fertilization. There were 15 treatments in total. The effects of irrigation, nitrogen application and their interaction on the grain filling characteristics and water and nitrogen use efficiency were explored, meanwhile, optimal water and nitrogen supply rates were solved by modeling.The results showed that t_e (grain-filling lasting time) and t_m (the time when maximum filling rate occurred) were affected by fertilization significantly, both of which increased first and then decreased as nitrogen application rates increased. t_e and t_m at N3 level were the largest, with an average of 43.9 and 24.6 days, which were 1.7 and 3.0 days longer than that of N0. The largest t_m value was obtained at W2N3 treatment, which happened 5.0 days later than W1N0 did. GF_max (maximum grain filling rate) and AG (average grain filling rate) exerted extremely significant correlation (r=0.841^**), 1000-kernel weight was extremely positive correlated with yield (r=0.791^**), t_e (r=0.755^**) and t_m (r=0.717^**). The highest grain yield and water use efficiency were obtained at W2N3 treatment with the maximum of 8 960 kg/hm² and 2.83 kg/m³. Water and nitrogen coupling efficiently improved yield of winter wheat by optimizing grain filling process. Optimal irrigation quota of sprinkler was 26~35 mm, nitrogen application rate was 193~204 kg/hm² (basal application 40% and topdressing 60% at jointing stage) achieved the goals of water-saving and yield-increasing.