Abstract: Salinity-alkalinity stress is an important factor of restricting crop high-yield and good quality, Ca²⁺ and H₂O₂ as signal molecules involved in crop response to stress. In order to understand whether Ca²⁺ is involved in the regulation of H₂O₂ on the seed germination and seedling formation in plant under saline-alkali stress, using subordinate function analysis method, we studied the effects of extracellular dissociation Ca²⁺ chelant EGTA, plasma membrane Ca²⁺ channel blockers LaCl₃, tonoplast Ca²⁺ release inhibitor ruthenium red(RR) and H₂O₂ on seed germination and seedling formation under saline-alkali complex stress(NaCl:Na₂SO₄:NaHCO₃:Na₂CO₃=12:8:9:1) with oat(Avena nude). The results showed that 25-200 mmol·L^-1 saline-alkali complex stress significantly inhibited seed germination and seedling formation of oat, and its inhibition was more obvious as the concentration was increased. While 0.001-2 mmol·L^-1 H₂O₂ could promote the seed germination and seedling formation of oat, and 0.5 mmol·L^-1 H₂O₂ significantly relieve the inhibition of 75 mmol·L^-1 saline-alkali complex stress to seed germination and seedling formation of oat. After EGAT treatment, combining with LaCl₃ and RR, the effect of H₂O₂ was decreased. Therefore, Ca²⁺ was involved in the signal transduction of seed germination and seedling formation of oat induced by H₂O₂ under saline-alkali mixed stress.