Abstract: A hydroponics experiment was conducted to study the effects of single and compound application of nitric oxide (NO) donor sodium nitroprusside (SNP) and salicylic acid (SA) on plant growth, photosynthetic parameters, membrane lipid peroxidation and the ascorbate-glutathione cycle (AsA-GSH cycle) in tomato cultivar (‘Qinfeng Baoguan’) seedling leaves under 100 mmol/L NaCl stress. Results showed that salt stress had significant effects on the growth, photosynthetic rate, and related indicators of reactive oxygen metabolism. Single or combined application of SNP and SA effectively alleviated the salinity damage of tomato seedlings, and the strongest effect was observed after applying a combination of SNP and SA. After 3-7 days of stress treatment, the PSⅡ maximal photochemistry efficiency (F_v/F_m), net photosynthetic rate (P_n), activities of ascorbate peroxidase (APX), glutathione reductase (GR) and droascorbic acid reductase (DHAR), and contents of reductive-form abscisic acid (AsA) and reduced glutathione (GSH) in leaves increased by 9.5%-15.3%, 25.5%-94.9%, 38.8%-67.5%, 15.2%-30.6%, 7.9%-41%, 4.4%-45.7%, and 13.8%-21.5%, respectively. Furthermore, the contents of H₂O₂, malondialdehyde (MDA), dehydroascorbic acid (DHA), oxidized glutathione (GSSG) and electrolyte leakage in leaves were reduced by 18.4%-40.4%, 35.2%-52.4%, 4.6%-26.3%, 14.8%-20.7%, and 23.1%-29.3%, respectively, compared with stress treatment. In conclusion, single or combined application of SNP and SA not only played a role in the stable operation of the AsA-GSH cycle, but also reduced membrane lipid peroxidation, promoted photosynthesis, enhanced plant growth and development, and improved seedling resistance by maintaining and coordinating the increase in related antioxidant enzyme activities and inhibiting the decrease in antioxidant content. Thus, a synergistic effect was observed after applying both SNP and SA.