Hydrogen sulfide (H₂S) is a novel endogenous gaseous signal molecule that regulates plant stress resistance. To investigate the alleviation effect and mechanism of exogenous hydrogen sulfide (H₂S) on tobacco seedlings growth under drought stress. This study adopted the method of nutrient solution hydroponics and used 15% polyethylene glycol (PEG6000) to simulate drought stress. Fluecured tobacco (Nicotiana tabacum cv. ‘Yuyan No.6’) was tested for their response following foliarspraying with sodium hydrosulfide (NaHS) at concentrations of 0, 0.1, 0.2 and 0.4 mmol·L^-1. Parameters measured included seedling growth, active oxygen metabolism, antioxidant enzyme activity, chlorophyll content and photosynthetic fluorescence characteristics. The results showed that： (1) tobacco seedling growth was significantly inhibited under drought stress.(2) Exogenous H₂S treatments significantly enhanced both shoot and root fresh weight, increased the total root length, total root surface area, average root diameter and root tip number of tobacco seedlings, enhanced chlorophyll relative content (SPAD), net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (G_s), maximal PSⅡ quantum yield (F_v/F_m), PSⅡ actual photochemical efficiency(Φ_PSⅡ) and photochemical quenching coefficient (qP), and reduced intercellular carbon dioxide concentration (C_i) and nonphotochemical quenching coefficient (NPQ), enhanced the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and decreased malondialdehyde (MDA) content and superoxide anion (O₂^-·) generation rate under drought stress. Foliar application with 0.20 mmol·L^-1 NaHS produced the largest growth promotion effects and drought stress alleviation.(3) Compared with drought stress alone, 0.20 mmol·L^-1 NaHS increased shoot and root fresh weight of tobacco seedling by 41.82% and 44.83%, enhanced SPAD, P_n, F_v/F_m, Φ_PSⅡ and qP by 62.88%, 246.96%, 8.43%, 23.71% and 10.84%, decreased C_i and NPQ by 25.79% and 22.68% enhanced the activities of SOD, POD and CAT by 50.67%, 140.59% and 71.68%, reduced MDA content and O₂^-· generation rate by 40.08% and 47.58%, respectively. These results indicated that exogenous H₂S positively stimulated tobacco seedlings to capture and convert solar energy, thus promoting seeding photosynthesis and growth, and also enhanced the adaptability of seedlings to drought stress by improving antioxidant capacity and reducing oxidative damage.