To explore the effects of spraying CaCl2 at different concentrations on physiological characteristics of apple seedlings under salt stress, two-year-old T337 seedlings were used as test materials, and the pot experiment was used to set 100 mmol/L NaCl(T1) and 100 mmol/L NaCl + four different concentrations of CaCl2 (5.0(T2), 7.5(T3), 10.0(T4), 12.5 mmol/L(T5)) treatment, watering with deionized water was used as the control(CK).Determine the chlorophyll content, photosynthetic and fluorescence parameters, antioxidant enzyme activity and osmotic adjustment substance content of each treatment group, and carry out correlation and principal component analysis. The results showed that with prolonged stress time, the catalase(CAT), peroxidase(POD), superoxide dismutase(SOD) of T337 leaves first increased and then decreased, malondialdehyde(MDA), intercellular CO2 concentration(Ci), proline(Pro) and relative conductivity(REC) showed a rising trend, initial fluorescence(F0), PSⅡ maximum light energy conversion rate(Fv/Fm) stomatal conductance(Gs) and the transpiration rate(Tr) showed a downward trend;compared with CK and T1, the variation amplitudes of T337 leaves after treatment with exogenous CaCl2 were all reduced, and there was a significant concentration effect. Among them, the relative chlorophyll content(SPAD), Pn, Tr, POD, F0 and SOD decreased the least under T4(10mmol/L) treatment, which was significantly higher than other treatment groups;MDA, REC and Ci increased the least, which was significantly higher than CK and lower than others processing group. Correlation analysis of 14 indicators showed that Pn was positively correlated with CAT, Tr, Gs, F0, Fv/Fm, ETR, SPAD, SOD and POD, and negatively correlated with Pro, MDA, Ci, and REC. Principal component analysis was performed on 14 related indicators after salt stress treatment, and 2 principal components with eigenvalues greater than 1 were extracted, and their eigenvalues were 11.190, 2.295, respectively;The first and second principal component variance contribution rates were 79.930%, 16.394%, respectively, the cumulative variance contribution rate reached 96.324%, which meets the analysis requirements. According to the ranking of principal component scores, the mitigation ability of exogenous CaCl2 to T337 salt stress was T4>T3>T2>T5 from high to low. Therefore, 10 mmol/L CaCl2 could improve the photosynthetic fluorescence characteristics of T337 rootstock leaves under salt stress, improve the antioxidant enzyme system and osmotic adjustment ability, and enhance the stability and permeability of biofilms to alleviate salt stress.