Abstract: Taking 4112，846 and 4112 × 846 as sample，grain filling rate in different filling stages was analyzed.Results showed that filling rate in different stages had significant difference between inbred lines.All samples had peak of filling rate after pollination 25 d，and 4112 × 846 was the biggest filling rate.It might be regarded as the critical period for filling from pollination 25 d to 50 d，this stage was a critical period for hybrid growth.In order to ensure high yield，management of maize hybrid should be strengthened，supply nutrient and water.