Abstract: 1) Medicago sativa seeds were soaked in two concentrations (0.1 and 1.0 mmol/L) of sodium nitroprusside (SNP) for 48 h. Samples of 50 seeds taken on 10 consecutive days were cultured in dishes under conditions of constant light and temperature at (25±1)℃.NaCl solution (6 mL 0.15%) was added to investigate the effects of exogenous nitric oxide on seed germination under NaCl stress. 2) The influence of the exogenous nitric oxide donor (SNP) at concentrations of 0.1 and 1.0 mmol/L on M. sativa seedling leaf oxidative damage under 0.15% NaCl stress were studied for 8 days of treatment. The treatments were, T1: CK (distilled water); T2: 0.15% NaCl; T3: 0.1 mmol/L SNP+0.15% NaCl; T4: 1.0 mmol/L SNP+0.15% NaCl. The results indicated that germination rate (P＜0.01), germination energy, germination index (P＜0.05) and vigor index (P＜0.05) of M. sativa seeds were dramatically promoted by SNP treatments during germination under 0.15% NaCl stress. The activities of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), were increased, which is consistent with the up-regulation of proline and soluble sugars, and with the down-regulation of O₂^- production, speed and content of malondialdehyde (MDA), H₂O₂ and chlorophyll in M. sativa seedling leaves compared with those under salt stress. Meanwhile, the protective ability of concentrations of 0.1 mmol/L was significantly better than those of 1.0 mmol/L.