A pot experiment was conducted for water control test of spring maize. Three water control levels (normal water supply, moderate drought, severe drought) and two periods (droughting, rewatering) were set up to research the effects of different degrees of drought stress and rewatering during seedling stage on light response curve, CO2 response curve, curve fitting parameters and antioxidant enzymes activities of spring maize. The results showed that the light radiation utilization capacity of spring maize leaves was decreased under drought stress. [1]Along with the increasing drought stress, maximum leaf net-photosynthetic rate (Pnmax), apparent quantum efficiency (AQY), light saturation point(LSP), the maximum electric transportation rate (Jmax), and even the maximum carboxylation rate (VCmax) of spring maize leaves were all decreased significantly, however, light compensation point (LCP), the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in leaves were apparently increased. After rewatering, the Pnmax, AQY, LSP, Jmax and VCmax under moderate drought stress in early stage were generally higher than those of normal water supply and moderate drought. However, the above parameters (except Jmax, VCmax ) under the severe drought did not reach the level of normal water supply, but higher than the severe drought. The SOD, POD and CAT activities had decreased, which still were higher than the normal water supply and drought level, and had a less decrement after severe drought stress. These results implied that a moderate drought hardening at the seedling stage could bring the higher antioxidant enzymes activities and remove the reactive oxygen species. Consequently, the reduced degree of membrane lipid peroxidation would make the membrane easier to be repaired after rewatering. These facts made the photosynthetic efficiency of the leaves produce a super-compensation effect. But after severe drought, the membrane repair was delayed, and the photosynthetic efficiency was just partially compensated. Hence, drought hardening should be limited in the level of medium drought for spring maize production in arid area northwest China, avoiding severe drought.