As global climate warms gradually, the intensification of drought not only inhibits plant growth but also seriously hinders the development of agriculture and animal husbandry. Recent research on exogenous H2S alleviating drought stress has mainly focused on crops, while studies using forage plant as experimental materials have mostly remained at the physiological mechanism against drought resistance, with fewer investigations into the metabolic mechanism. Dahurian lespedeza (Lespedeza davurica), a high-quality forage grass for controlling soil erosion, exhibits excellent characteristics such as tolerance to poor soil and salt-alkali resistance. However, due to its wide distribution in arid and semi-arid regions, its seedlings are vulnerable to drought stress during the seedling stage. Therefore, using NaHS as an exogenous H2S donor, this study applied exogenous H2S via foliar spraying, setting two NaHS concentrations (0 and 0.01 mu molL-1) and four time points (0 day, 10 days, 20 days, 30 days) to form 12 treatment groups, each with 16 repetitions. The results showed that long-term drought stress caused excessive ROS accumulation, increased MDA content, and decreased RWC in seedlings, severely inhibiting their growth. After the spraying of 0.01 mu molL-1 exogenous H2S, the activity of antioxidant enzymes in seedlings significantly increased, and isoflavonoid biosynthesis and biosynthesis of various alkaloids were significantly upregulated, among which the key secondary metabolites Medicarpin and Isatin were significantly upregulated. These secondary metabolites effectively scavenged ROS, increased relative water content, and enhanced the content of osmotic adjustment substances (proline, soluble sugars, soluble proteins), thus protecting cell membranes from damage and enhancing the drought resistance of seedlings. Through physiological mechanism and metabolomics analysis, this study revealed the response mechanism of Lespedeza davurica seedlings to drought stress and the alleviation mechanism of exogenous H2S, identifying key secondary metabolites Medicarpin and Isatin. This provides a theoretical basis for researching drought resistance mechanisms in forage plants and optimizing cultivation practices in arid and semi-arid regions.