Salinity causes yield and quality losses in agricultural production and therefore great economic losses around the world. Hydrogen sulfide (H2S) is known to play a crucial role to ease physiological and metabolic processes in plants, and also increases the tolerance of the plant against many abiotic stress conditions. In this study, we investigated the effects of H2S treatments (0, 25, 50, 75 and 100 µM NaHS were applied as H2S donor) to the tomato seedlings to alleviate the harmful effects of salt stress (0, 75 and 150 mM NaCl). There was a significant decrease in plant growth and development in parallel with the increased salt level. Visible changes in plant development were observed after the dose of 75 mM NaCl in the tomato seedling. The effects of different doses of exogenous H2S treatment were found to be significant. H2S treatment increased the stress tolerance in tomato seedlings by arranging the mineral element and hormone content. Furthermore, H2S relieved the effect of stress in plants by increasing photosynthetic activity (photosynthesis rate (Pn), transpiration rate (Tr), stomatal conductivity (gs) and intercellular CO2 concentration (Ci)) of the plant. In addition, the effect of H2S on salt stress tolerance in tomato seedlings may be due to its positive effect on mineral element contents. As a result, based on the beneficial effects of H2S in tomato seedlings under salt stress, this treatment can be considered as an alternative resilience method for cultivation in saline soils or irrigation with low quality waters.