[Objective] The high concentration of salt in soil seriously affected the yield and quality of Cucurbita pepo L, and exogenous silicon could effectively alleviate the damage of salt stress to crops.To explore the protective mechanism of exogenous silicon on water metabolism and photosynthesis of Cucurbita pepo L. seedlings under salt stress, and to provide theoretical reference for salt resistance of C. pepo. [Methods] Taking“Hanlu 7042” C. pepo variety as test material, through hydroponic experiment, four treatments were set: Control , silicon treatment(0.3 mmol/L Na2SiO3·9H2O), salt stress(150 mmol/L NaCl), salt stress + silicon treatment(0.3 mmol/L Na2SiO3·9H2O + 150 mmol/L NaCl). After 10 days of treatment, the root morphology, root activity, leaves water content, leaves water potential, photosynthetic parameters, chlorophyll content, chlorophyll fluorescence parameters and expression of plasma membrane aquaporin gene were determined. [Results]Salt stress significantly inhibited the growth of C. pepo seedling roots, decreased root activity, leaf water content, leaf water potential and transpiration, and salt stress also destroyed the photosynthetic system of the plant, net photosynthetic rate, stomatal conductance, chlorophyll content and PSII photochemical efficiency were significantly decreased. Exogenous silicon significantly improved the root morphology and activity of C. pepo seedlings under salt stress by promoting the genes PIP1;2, PIP1;3, PIP1;5, PIP1;7, PIP2;1, PIP2;4, PIP2;6, PIP2;8. The expression of PIP2;9 and PIP2;12 improved the water status in plant, which showed that leaf water content and leaf water potential were increased, and transpiration was enhanced, the exogenous silicon also increased the stomatal conductance, chlorophyll content, net photosynthetic rate, PSII maximum photochemical efficiency, PSII actual photochemical efficiency and photochemical quenching coefficient, the photosynthesis of seedlings under salt stress was enhanced by decreasing intercellular carbon dioxide concentration and non-photochemical quenching coefficient. [Conclusion] The addition of 0.3 mmol/L silicon could improve the water metabolism and photosynthesis of C. pepo seedlings under salt stress, and thus enhance the ability of C. pepo seedlings to resist salt stress.