Abstract: Apple rootstock M26 seedlings were grown in nutrient solution to study the effects of five concentrations of SNP(50,100,150,200 μmol·L^-1 and 300 μmol·L^-1) on chlorophyll content, photosynthetic properties, antioxidant enzymes, reactive oxygen species and membrane lipid peroxides, and osmoregulatory substances under salt stress, in order to provide reference for enhancing the salt tolerance of M26 seedlings.The results showed that the photosynthetic pigment content was significantly reduced, photosynthesis was inhibited, H₂O₂ and MDA content increased, and antioxidant enzyme activity was also inhibited in general, while osmoregulatory substance content increased in M26 seedling leaves under salt stress.After exogenous spraying of 200 μmol·L^-1 SNP,the photosynthetic pigment content, photosynthetic efficiency and antioxidant enzyme activity of M26 seedlings were significantly increased, the contents of H₂O₂ and MDA were significantly decreased, and the contents of soluble protein and Pro were further increased.It could be seen that exogenous addition of NO could alleviate the damage caused by salt stress to M26 seedlings to a certain extent, thus improving the salt tolerance of seedlings and promoting seedling growth.