In order to clarify the effects of nitrogen application rate on grain filling characteristics of winter wheat,field experiments were carried out during 2010~2011 in Wen County of Henan Province with two cultivars PA-8 and YM49 198 as experimental materials.The experiment was designed as randomized block arrangement,with the application rates of N120,N180,N240 and N360 kg·hm-2,respectively,indicated as N120,N180,N240,N360.The results showed that grain weight and yield could be increased significantly under nitrogen application conditions.The reason could be mainly due to the extension of active grain filling period and increasement in the filling rate of winter wheat.Nitrogen application could increase significantly the days of the rapid growth period in the filling,and those of N240 of the two cultivars accounts for 58% in the contribution rate on the final grain weight.Besides,nitrogen application improved the rate at the filling stage,and the research indicated that N180 and N240 treatments were much more obvious than others.The result showed that the nitrogen had the role of adjusting the filling rate,active grain filling growing season,and the three divisions of filling period,and finally increased grain weight.