In order to reveal the effects of CO₂ enhancement on the physiological characteristics of maize seedlings under different irrigation strategies，the effects of CO₂ enhancement on endogenous hormone content，photosynthesis and chlorophyll fluorescence，reactive oxygen species accumulation and antioxidant mechanism under sufficient irrigation，alternating irrigation and water deficit irrigation were analyzed.The results showed that，alternative and deficit irrigation promoted the increase of abscisic(ABA)/zeatin-riboside(ZR)，and then induced stomatal contraction，which significantly reduced transpiration，but only reduced photosynthetic assimilation under alternative irrigation in a certain extent.Finally，alternating irrigation induced the increase of leaf water use efficiency and maintained the stability of maximal efficiency of PSⅡ(Fv /Fm).Stomatal contraction also induced excess generation of O₂·- and H2O₂ in leaves.Alternative irrigation could maintain the stability of malondial-dehyle (MDA) content by increasing the activity of leaf antioxidant enzymes including catalase (CAT)，peroxidase (POD)，and superoxide dismutase (SOD)，so as to avoid the possible damage of membrane lipid peroxidation.The enhancement of CO₂ concentration decreased ABA/ZR，accelerated electron transfer rate，increased photosynthetic rate and leaf water use efficiency.In addition，the enhancement of CO₂ concentration inhibited the generation of O₂·- and H2O₂ in leaves under different irrigation strategies in a certain extent，and the activities of leaf antioxidant enzymes，such as SOD，CAT and POD，decreased accordingly.Finally，the enhancement of CO₂ concentration reduced the level of membrane lipid peroxidation under different irrigation strategies，which is conducive to crop growth.