In order to investigate the physiological mechanism of sweet cherry rootstock under NaCl treatment, we studied the osmotic regulation substances, antioxidant enzyme activities, photosynthetic characteristics and chlorophyll fluorescence parameters of sweet cherry rootstocks ‘Gisela 6’ and ‘Colt’ seedlings under different concentrations (0, 50, 100, 150 mmol·L^-1) of NaCl solution with potted 1-year-old seedlings. The results showed that: (1) NaCl treatment promoted the accumulation of osmotic regulatory substances such as soluble sugar, soluble protein and proline in sweet cherry rootstock leaves. (2) With the increase of NaCl concentration, SOD activity in sweet cherry rootstock leaves showed an increasing trend, while POD activity increased first and then decreased. (3) With the increase of NaCl concentration, the net photosynthetic rate (P_n) and stomatal conductance (G_s) decreased gradually, while the intercellular CO₂ concentration (C_i) increased gradually in sweet cherry rootstocks. Non-stomatal limitation was the main factor for the decrease of P_n. (4) NaCl treatment inhibited the maximum photochemical efficiency (F_v/F_m), photochemical quenching coefficient (qP) and electron transfer efficiency (ETR), and increased non-photochemical quenching coefficient (NPQ) in sweet cherry rootstock leaves. In conclusion, salt stress destroyed the photosynthetic mechanism of sweet cherry rootstocks, inhibited the electron transfer rate and photochemical quantum efficiency, and reduced the utilization rate of light energy, resulting in the decrease of photosynthetic rate. Under the condition of salt stress, sweet cherry rootstocks can improve the adaptability to salt stress mainly increasing the content of osmotic regulatory substances and increasing the activity of antioxidant enzymes, relieving osmotic stress and reducing oxidative damage. ‘Gisela 6’ showed stronger adaptability and salt tolerance under salt stress. Sweet cherry rootstocks showed obvious symptoms of victimization when treated with more than 100 mmol·L^-1 NaCl.