Abstract: This study investigated the alleviation mechanism of exogenous calcium chloride（CaCl₂）on Bougainvillea spectabilis Willd. under NaCl stress, aiming to provide a theoretical basis for mitigating salt damage in Bougainvillea in saline-alkali regions and enriching plant landscapes in coastal saline-alkali areas. Potted Bougainvillea plants were used as experimental materials, with one control group（CK）and four treatment groups. After subjecting the plants to stress treatment with a 150 mmol·L⁻¹ NaCl solution, exogenous calcium chloride（CaCl₂）solutions at concentrations of 0 mmol·L⁻¹（CK1）, 50 mmol·L⁻¹（T1）, 100 mmol·L⁻¹（T2）, and 150 mmol·L⁻¹（T3）were applied to irrigate the salt-stressed Bougainvillea plants. Growth and physiological-related indicators were measured, and a comprehensive evaluation was conducted using principal component analysis and membership function analysis to identify the optimal CaCl₂ concentration for alleviating salt stress in Bougainvillea. The results indicated that with the extension of salt stress duration, the root length, root diameter, net photosynthetic rate（Pn）, and catalase activity（CAT）of Bougainvillea spectabilis significantly decreased, while the proline content（PRO）, superoxide dismutase activity（SOD）, peroxidase activity（POD）, malondialdehyde content（MDA）, 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, POD, SOD, and CAT of Bougainvillea spectabilis initially increased and then decreased with the increasing dosage of CaCl₂, while MDA and REC initially decreased and then increased. Compared with CK and CK1 treatments, the variation amplitude of each index of Bougainvillea spectabilis under exogenous CaCl₂ treatment was reduced, and a clear dose-effect relationship was observed. Specifically, the application of an appropriate dose of exogenous calcium chloride can alleviate the damage caused by salt stress to Bougainvillea spectabilis to a certain extent, while high levels of CaCl₂ can cause damage. Among them, the treatment with 100 mmol·L⁻¹ CaCl₂ showed the best effect on enhancing the salt tolerance of Bougainvillea spectabilis.