The effects of exogenous hydrogen sulfide (H₂S) on relative water content, membrane lipid peroxidation, reactive oxygen species, antioxidant enzyme activities, AsAGSH cycle metabolism, and antioxidants were investigated with white clover (Trifolium repens) under drought stress induced by PEG6000, which reveals the physiological mechanism of H₂Sregulated drought tolerance in white clover. The results showed that: (1) the plants treated with 0.2 mmol/L sodium hydrosulfide (NaHS), a H₂S donor, maintained higher leaf relative water content and lower electrolyte leakage and MDA content under drought stress as compared to the plants without the pretreatment with NaHS. (2) Similarly, the exogenous NaHS effectively improved SOD, CAT, POD activities and accelerated AsAGSH cycle metabolism via the improvement of the key enzyme activities (APX, DHAR, MDHAR and GR), AsA and GSH content. (3) The application of NaHS also increased flavonoid, total phenols and proanthocyanidins contents in leaves of white clover in a period of time, followed by decreases in the generation rate of O^-·₂ and H₂O₂ content in response to drought stress. Therefore, this study suggests that exogenous H₂S can improve drought tolerance of white clover seedlings through enhancing the leaf antioxidant defense system.