Abstract 【Objective】In order to explore the physiological mechanism of exogenous 2,4-epibrassinolide (2,4-EBR) in common bean (Phaseolus vulgaris L.) seedlings under saline-alkali stress conditions.【Methods】Using ''Shanxi Red Common Bean'' as the test material, we studied the effects of saline-alkali stress at 100mmol/L (50mmol/LNaCl+50mmol/LNaHCO3, XP), effects of exogenous spraying of 0.1 mg/L 2,4-EBR and 4.0 mg/L Brassinozole (BRZ) on the growth, photosynthetic gas parameters, antioxidant enzyme activity and osmotic adjustment substance content of common bean seedlings , and perform correlation and principal component analysis.【Results】Under saline-alkali stress, common bean leaves curled and withered, and plant height, leaf area, main root length, synthetic pigment content, net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) all decreased significantly (P<0.05) , proline (Pro), soluble sugar (SS) content and superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbic acid peroxidase (APX) activities, Relative conductivity (REC), malondialdehyde (MDA) and intercellular carbon dioxide concentration (Ci) were significantly increased (P<0.05). Exogenous spraying of 2,4-EBR can alleviate the wilting and curling of leaves caused by salt-alkali stress, and the plant growth condition gradually improves.?At the same time, it effectively reduces the REC, MDA and Ci of seedling leaves, and significantly increases plant height, leaf area, Primary root length, Pro, SS, Pn, Tr and Gs as well as SOD, POD, CAT and APX activities, but these salt-alkali resistance effects of common beans induced by exogenous 2,4-EBR were reversed after adding BRZ.【Conclusion】 Exogenous 2,4-EBR treatment can reduce membrane lipid peroxidation damage caused by salt-alkali stress by increasing antioxidant system enzyme activity and osmotic adjustment substance content in common bean leaves. It effectively removes the non-stomatal limiting factors that weaken the photosynthesis of common bean seedlings under saline-alkali stress, maintains the photosynthetic activity of the seedlings, promotes seedling growth, and enhances the salt-alkali resistance of common bean seedlings.