CO2 capture and storage (CCS) has the risk of CO2 leakage, and this leakage always increases soil CO2 concentration, and the long-term CO2 stress damages crop production in farmland. Using maize, the growth characteristics, such as plant height and yield, and physiological indexes (osmoregulation substances and antioxidant enzymes) were explored under different simulative CO2 leakage conditions. Further, the relationship between maize physiological indexes and soil CO2 concentration was analyzed, showing that soil CO2 stress inhibited maize growth to a certain extent, resulting in shorter plants, thinner stems and lower kernel yield. With an increase in soil CO2 concentration, the contents of malondialdehyde, soluble sugar and soluble protein in maize leaves increased; with continuing stress, the increase rate of malondialdehyde was greatly augmented, whereas the increase rates of soluble sugar and soluble protein decreased. With extended CO2 stress, the activity of the enzyme superoxide dismutase (SOD) increased continuously, while the activities of catalase and peroxidase first increased and then decreased. Superoxide dismutase activity was closely correlated with soil CO2 concentration (r = 0.762), and responded quickly to the change of soil CO2 concentration (R2 = 0.9951). Therefore, SOD plays an important role in maize resistance to soil CO2 stress. This study will help further understanding of the mechanism of maize tolerance to soil CO2 stress, providing a theoretical basis for agricultural production in CCS project areas.