Alleviatedeffects of exogenous nitric oxide on oxidative damage in Malus hupehensis (Pamp.) Rehd.seedlings were studied under water stress.The results showed that 100-500 μmol·L^-1 SNP(sodium nitrop russide,NO-donor) can alleviated the different degree oxidative damage under water stress,with the activities of superoxide ismutase(SOD),peroxidase(POD),catalase(CAT),ascorbate peroxidase(APX) and the content of ascorbic acid(ASA) were increased in seedling’s leaves.The study showed that 300 μmol·L^-1 SNP have the significantly effects and relatively high concentration(700 mmol · L^-1 SNP) can not play a relief role,meantime there are certain toxic effectson M.hupehensis seedings.