Abstract: In order to provide a reference for alleviating the salt damage of Bougainvillea spectabilis in the saline-alkali areas and enriching the plant landscape in the coastal saline-alkali areas, the alleviation mechanism of exogenous calcium chloride (CaCl₂) on Bougainvillea spectabilis under NaCl stress was explored. By taking the potted Bougainvillea spectabilis as the experimental materials, one control group (CK) and four treatment groups were set up. After subjecting the plants to the stress treatment with 150 mmol·L⁻¹ NaCl solution, the exogenous calcium chloride（CaCl₂）solutions at the concentrations of 0 mmol·L⁻¹ (CK1), 50 mmol·L⁻¹ (T1), 100 mmol·L⁻¹ (T2) and 150 mmol·L⁻¹ (T3) were added to irrigate the salt-stressed Bougainvillea spectabilis. Some indexes related to the growth physiology were determined, and the comprehensive evaluation was carried out by combining with the principal component analysis and membership function analysis. Then, the concentration of calcium chloride solution with the best alleviating effect on salt stress of Bougainvillea spectabilis was screened out. The results showed that with the extension of salt stress duration, the root length, root diameter, net photosynthetic rate (Pn), and catalase (CAT) activity of Bougainvillea spectabilis significantly decreased, while the proline content (PRO), superoxide dismutase (SOD) activity, peroxidase (SOD) activity , malondialdehyde (MDA) content, and relative electrical conductivity (REC) significantly increased, indicating an intensified degree of membrane lipid peroxidation. After the application of CaCl₂, the root length, root diameter, Pn, PRO content, POD activity, SOD activity and CAT content of Bougainvillea spectabilis initially increased and then decreased with the increase of CaCl₂ dosage, while MDA content and REC initially decreased and then increased. Compared with CK and CK1 treatments, the variation amplitude of each index of Bougainvillea spectabilis under the exogenous CaCl₂ treatment was reduced, and a clear dose-effect relationship was observed. Specifically, the application of appropriate dose of exogenous calcium chloride could alleviate the damage degree caused by salt stress to Bougainvillea spectabilis to a certain extent, while the high levels of CaCl₂ could cause the damage. Among them, the treatment with 100 mmol·L⁻¹ CaCl₂ showed the best effect on enhancing the salt tolerance of Bougainvillea spectabilis.