Abstract: In order to illuminate the regulating mechanism of gas signal hydrogen sulfide（H₂S）on reactiveoxygen species（ROS）metabolism of naked oat（Avena nuda）under saline-alkali stress,and to screen anddetermine the optimal application period and concentration of H₂S,the effect of spraying Na HS(H₂S donor;0,25,50,100,200 and 400 μmol·L^-1) at different periods（seedling stage,jointing stage,heading stage,flowering stage and filling stage）on the H₂S content,H₂S production related enzyme activityof L-cysteinedesulfhydrylase（LCD）and ROS metabolism-related enzyme activities and substance contents in leaves of soilpotted naked oat under 3.0 g·kg^-1 salt-alkali mixed stress（NaCl∶Na₂SO₄∶NaHCO₃∶Na₂CO₃ molar ratio was 12∶8∶9∶1）were carried out respectively.The results showed that spraying period,Na HS concentration and their interactionhad significant effects on the content of H₂ S,superoxide anion(O₂^-.),hydrogen peroxide（H₂O₂）,malondialdehyde （MDA）,ascorbic acid（As A）and glutathione（GSH）,and the activities of LCD,superoxide dismutase（SOD）,catalase（CAT）,peroxidase（POD）,ascorbic acid peroxidase（APX）and glutathione reductase（GR）in nakedoat leaves under salt-alkali stress respectively.Compared with spraying 0 μmol·L^-1 NaHS,spraying a certainconcentration of Na HS increased the contents of H₂S,As A,GSH and the activities of LCD,SOD,CAT,POD,APX and GR,and reduced the accumulation of O₂^-.,H₂O₂ and MDA respectively.However,the optimal sprayingperiod and NaHS concentration of the above indexes were different.Comprehensive analysis of membershipfunction showed that spraying 25-200 μmol·L^-1 NaHS at the seedling stage and jointing stage had the highest thecomprehensive evaluation value（D）.It indicated that spraying 25-200 μmol·L^-1 Na HS at the seedling-jointstage improved the ROS scavenging ability,alleviated the oxidative damage of salt-alkali stress on naked oats.