In this study, the responses of CaCl₂ addition to seedlings of Cornus hongkongensis subsp. tonkinensis, which were subjected to 3‰ salt stress, were evaluated by physiological indexes, including seedling growth, phytosynthetic pigment content, photosynthetic gas exchange parameters and osmotic regulation substance content, etc. The main results were: (1) 3‰ sea salt stress significantly inhibited seedling growth, increased the contents of malondialdehyde (MDA), soluble sugar, soluble protein, proline and activity of superoxide dismutase (SOD), increased photosynthetic pigment synthesis, photosynthetic parameters including intercellular carbon dioxide concentration (C_i), net photosynthetic rate (P_n), stomatal conductance (G_s) and transpiration rate (T_r). (2) For alleviating treatments with CaCl₂ to stressed seedlings by 3‰ salt, application of CaCl₂ with low concentration (10-20 mmol·L^-1) to stressed seedlings reduced the salt damage rate and mortality rate, decreased SP content and further promoted leaf and plant biomass of seedlings. Correspondingly, MDA content in alleviated seedlings was significantly decreased at medium and low concentrations of CaCl₂. Alleviator with medium concentration (30 mmol·L^-1) promoted the synthesis of chlorophyll B and total photosynthetic pigment. C_i, P_n, G_s and T_r in stressed seedlings were effectively enhanced in all alleviating treatments. Comparatively, the effects at low concentration of CaCl₂ on alleviating stress were significantly superior to that at medium and high concentrations. CaCl₂ application with high concentration (40 mmol·L^-1) did not relieve all measured physiological indexes stressed by 3‰ sea salt. In conclusion, the application of low concentration of CaCl₂ (10-20 mmol·L^-1) could reduce the damage of salt stress by reducing the decomposition of photosynthetic pigments, improving the photosynthetic rate, inhibiting the accumulation of reactive oxygen species, and maintaining the stability of plasma membrane, thus reduce salt damage rate and mortality of seedlings, and effectively alleviate the inhibition effect of salt stress on C. hongkongensis subsp. tonkinensis.