【Objective】 The response of maize root characteristics on population density were studied.【Method】 Four maize varieties Yifeng29, Zhengdan958, Xianyu335 and Xianyu420 were used as the tested materials. The number of brace root, dry mass and protective enzyme activities of root were measured, and the effects of population density on basic characteristics of root were determined.【Result and conclusion】 With the increase of population density, the number of brace root, dry mass and root activity increased first and then decreased, and the peaks occurred under different treatments. Protective enzyme activities of root were different with varieties, and MDA contents increased with the increase of population density. The percentage of lodging, the number of brace root and dry mass of root of Zhengdan958 were the biggest, while Xianyu335 had a higher protective activities.