A pot experiment was conducted to study the effects of simulated moderate drought in whole growth period on the grain yield and root physiological traits of drought-tolerant maize variety JK-628 and drought-sensitive maize variety ND-95. Compared with the control, the grain yield of JK-628 and ND-95 under the stress of moderate drought was decreased by 33.7% and 62.3%, respectively. Under drought stress, the root biomass of the two varieties decreased, with the maximum value appeared ahead. The root/shoot ratio of JK-628 increased at early growth stage but decreased at late growth stage, while that of ND-95 increased all along. ND-95 had a larger decrement of root activity than JK-628. The root SOD activity in drought-stress plants was higher in prophase but lower in anaphase, compared with that in the control, and the time of SOD activity begun to lower was later for JK-628 than for ND-95. The root MDA content in drought-stress plants was increased, and the increment was much higher for ND-95 than for JK-628. In addition, the root soluble protein content in drought-stress plants was decreased, and ND-95 had a larger decrement than JK-628. In a word, under drought stress, the root activity, SOD activity, and soluble protein content of JK-628 were higher than those of ND-95, which could slow down the root aging process and prolong the root functional period, possibly being one of the important factors of getting high yield of drought-tolerant maize under drought stress.