Abstract: Lodging was the factor of limiting high yield of summer maize.The field experiment and field demonstration were conducted to study the effect of four chemical regulation medicines (Aifeng, Yu Huangjin, Ethephon, Jindele) with different period and different planting density on plant growth, lodging resistance and yield of summer maize. The conclusions were as follow. With the increasing of planting density the yield of summer maize increased, the plant height and ear height increased, the stem roughness decreased, the ratio of length and thickness became larger, the risk of lodging increase gradually, increasing plant density can significantly decrease the effect of chemical regulation on lodging resistance. In Yellow and Huai River Region , appropriate plant density of summer maize was 60000-75000 plants/hm2. Chemical regulation decreased plant height at 6 leaf stage uniformly, which was used to shape ideal coefficient of ear height and the ratio of stem length and thickness. The lodging resistance was the best when using chemical regulation at 6 leaf stage, followed by 8 leaf stage, 10 leaf stage was the worst. In addition, the impact on yield was the least when using chemical regulation at 6 leaf stage while that was the largest when using chemical regulation at 10 leaf stage. So 6 leaf stage was the best period of chemical regulation.