In order to clarify the mechanism of silicon enhancing plant salt resistance,Cucumis sativus L.cv ‘Jinyou No.1’ was grown in the hydroponic solution with silicon and NaCl.The effects of silicon on growth,photosyntheisis,osmotic adjustment and ion accumulation in cucumber seedlings were investigated.(1)Application of silicon alone had no effects on cucumber growth,while it partly reversed the salt-induced reduction in plant growth,chlorophyll content,water content,photosynthesis,stomatal conductance and transpiration.(2)The osmotic potential of silicon application was lower at beginning of salt stress,then became higher than salt alone application.Meanwhile,the osmolytes,especially,the sucrose levels,but not the proline,were significantly increased than that without silicon application under salt stress.The soluble protein content was not affected by silicon application.(3)Na⁺ concentration was increased while K⁺ concentration and K⁺/Na⁺ ratio were decreased in salt-treated plants.While,this tendency was partly reversed by silicon application,especially in the leaves.It can be concluded that silicon application decreases Na⁺ toxicity and improves the water status in plant,which allows a higher photosynthesis and growth rate,lead to salt tolerance.Osmotic adjustment,which has little effect at the beginning of salt stress,is not the main factor of silicon improving the salt tolerance.