As the third major grain crops behind the wheat and rice, maize (Zea mays L.) plays an important role in the source of food and industrial raw materials. In arid and semi-arid regions of northwest China, the abundant solar energy provide a tremendous potential of maize yields, but it is out of harmony with rainfall resource insufficient, especially in the early-stage (sprout and seedling stages) of summer maize. As a plant organ in absorbing soil water and minerals, crop roots could change the distribution, structure, and protective enzyme contents to responding the drought stress. However, little is known about how these indexes affect the plant ability comprehensively. To study the effects of sustained water stress on maize root structure and physiological characteristics, and reveal the drought resistance mechanism for early-stage (sprout and seedling stages) of summer maize. a maize (Liyu 18) pot experiment contains four water treatments was conducted: (i) mild water stress (LS, 70% of the field moisture capacity); (ii) moderate water stress (MS, 50% the of field moisture capacity); (iii) severe water stress (SS, 30% of the field moisture capacity); (iv) and normal water supply (CK, 85% of the field moisture capacity) as the control. The results showed that the biomasses of aboveground part and root were both significantly (P < 0.05) decreased under water stress treatments in seedling stage of summer maize, and root structure also significantly (P < 0.05) difference. And the length, surface area, volume, and dry weight of maize root were all decreased with the increase of water stress. Compared with CK, fine root length (diameter, 0.05-0.25 mm) and root surface area ratio significantly (P < 0.05) increased in LS and MS, and thick root length (diameter > 0.50 mm) and root surface area ratio decreased in SS. Root-shoot ratio, root activity, and malondialdehyde content increased with the increase of water stress, which could improve the drought resistance of crops. The crop allocated more photosynthetic product to the roots to relieve the long time water stress, so the root-shoot ratio decreased with the extending of stress time. Compared with CK, the soluble protein content of maize root under MS and SS treatments was significantly (P < 0.05) decreased with a reduction of soil moisture in seedling stage, which may be attributed to the protein synthesis was limited by the water stress. The results also showed that the protective enzyme activity of maize root increased by the soil water stress to reduced the damage of the active oxygen accumulation. The superoxide dismutase (SOD) of summer maize root was more sensitive to soil water stress than catalase (CAT) and peroxidase (POD), and the root reduced the oxidative damage mainly depend on CAT under LS, POD under MS, and SOD under SS. Under the SS, the enzyme activity of maize root decreased with the extending of stress time. In general, for early-stage (sprout and seedling stages) of summer maize, the adverse effects of water stress can be reduced comprehensively by the increased of root-shoot ratio, improved of root and protective enzyme activity, and decreased the amount of osmotic regulation substances (i.e. soluble protein).