The study was conducted in nutrient solution to investigate the effects of exogenous nitric oxide (NO) on growth of cucumber seedlings, active oxygen metabolism and photosynthetic characteristics in cucumber leaves under 50mmol•L^-1 NaCl stress. The results showed that 10-400 μmol•L^-1 exogenous sodium nitroprusside (SNP), a nitric oxide donor, especially 100 μmol•L-1SNP, significantly alleviated the injury to seedlings and increased seedling growth, activity of SOD, POD, CAT, APX, the content of photosynthetic pigment and proline under 50mmol•L^-1 NaCl stress. Similarly, net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) were also increased significantly. However, exogenous nitric oxide markedly decreased membrane permeability, rate of O^•-₂ production, the content of MDA and H₂O₂, intercellular CO₂ concentration (Ci) under 50mmol•L-1 NaCl stress.