In this study, the salt-tolerant chrysanthemum cultivar ‘Xuanqiu Jiangyue’ and the salt-sensitive cultivar ‘Xuanqiu Duran’ were used as test materials, and NaCl and NaHCO3 were mixed with 1∶1 mass ration to prepare a compound saline-alkali solution at the concentration of 100 mmol/L. The seedlings of chrysanthemum were treated with saline-alkali stress, and the leaves were sprayed with four concentrations(0.001, 0.010, 0.100, 1.000 mg/L) of exogenous brassinolide(BR) with the H2O as the control(CK). The effects of BR on the growth and physiological indexes of chrysanthemum seedlings under saline-alkali stress were studied. The results showed that compared with the control, the relative water contents of the leaves of ‘Xuanqiu Jiangyue’ and ‘Xuanqiu Duran’ increased by 8.11% and 16.95%, respectively, and the chlorophyll contents increased by 9.55% and 13.97%, respectively, when sprayed with 0.100 mg/L BR under saline-alkali stress. The relative conductivities decreased by 27.63% and 24.69%, respectively. The contents of malondialdehyde(MDA) decreased by 41.24% and 67.38%, respectively. The contents of proline(Pro) increased by 86.49% and 69.46%. The activities of catalase(CAT) increased by 16.25% and 18.14%, respectively. The activities of peroxidase(POD) increased by 46.15% and 68.38%, respectively. The activities of superoxide dismutase(SOD) increased by 12.36% and 16.32%, respectively. The activities of ascorbate peroxidase(APX) increased by 76.88% and 95.04%, respectively. In summary, exogenous spraying of 0.100 mg/L BR could better promote the growth and development of chrysanthemum seedlings under saline-alkali stress, improve the activity of antioxidant enzymes and the stability of biofilms, thereby alleviate the damage of saline-alkali stress to chrysanthemum seedlings, and the alleviation effect of salt-alkali damage of salt-sensitive variety ‘Xuanqiu Duran’ was more obvious.