Using the maize variety Xianyu 335 and self-made plant growth regulator as experimental material, field experiments were conducted with four chemical regulation treatments（T_CK: no spray; T₈: spray at the eight-leaf; T₁₅:spray at the fifteen-leaf; T₈₊₁₅: twice spray at eight and fifteen leaf）and two planting densities（60 000 plants/ha as normal density and 90 000 plants/ha as high density, recorded D₆ and D₉, respectively） to discuss the effect of postponing chemical regulation stage to fifteen-leaf on grain filling characteristics of maize under different densities.The grain filling process was fitted by Logistic equation and the relationship between grain weight and characteristic parameters of grain filling was analyzed. The results showed that compared with the conventional chemical control treatment, T₁₅ and T₈₊₁₅ could increase the grain filling rate. The grain filling rate at the rapid growth stage of grain weight increased by 35.1% and 15.5% respectively under the conventional density, and increased by 5.0% and 3.3% respectively under the high density. The active grouting time and effective grouting time of T₁₅ under high density were extended by 2.8 d and 4.0 d respectively compared with T₈. The grain filling duration could be prolonged and the grain filling rate could be increased by postponing chemical regulation.