A sand culture experiment was conducted in greenhouse to study effects of exogenous nitric oxide donor(SNP) on growth, photosynthetic characteristics and alkaloids contents of Catharanthus roseusseedlings under 50 mmol L^-1 NaCl stress. Results show: (1) 0.1 mmol L^-1 SNP was the highest in effect of alleviating the stress caused by 50 mmol L^-1 NaCl, and significantly increased fresh weight, dry weight, Pn, Gs, Tr and POD activity by 18.8%, 13.9%, 20.7%, 19.1%, 8.5% and 32.6% respectively, but decreased Ci by 10.3% as against Treatment S₁ (50 mmol L^-1 NaCl). (2) In Treatment S₄, where the concentration of SNP increased to 0.5 mmol L^-1, the TDC activity, total indole alkaloids, Vinblastine, Catharanthine, Vincristine and Vindolin contents of the Catharanthus roseuswere the highest, compared with Treatment S1, they increased 33.4%, 26.9%, 32.3%, 27.4%, 68.8% and 50.2% respectively. To sum up, 0.1 mmol L^-1SNP is the best at increasing photosynthesis, promoting growth and raising biomass, however 0.5 mmol L^-1 SNP is the best at improving synthesis of total indole alkaloids and four main kinds of alkaloids.