Abstract: Based on a 25-year allocated experiment at the Experimental Farm in Hengshui, the process of grain filling in summer maize was studied in 2006 .The results indicated that under the condition of wheat and maize rotation, grain number increased with fertilizer rates. Chemical fertilizer, straw and their combinations increased grain number by 103.6–161.6%, 11.9–58.9% and 105.7–159.6%, respectively. The grain dry weight accumulation could be described by logistic model, and the correlation coefficient was over 0.99. The filling period was increased by more fertilizer application, but the maximum filling rate was not significantly influenced.