With cucumber cultivar ‘Chunqiuwang No.2’ as test material,the effects of four root-zone temperature gradient (20 ℃,25 ℃,30 ℃,35 ℃) on the growth,antioxidant enzymes and osmotic substance of cucumber seedlings under hydroponic cultivation were investigated.The results showed that:(1)The differences of plant height,stem diameter,leaf area,shoot and root fresh weight are significant between 25 ℃ treatment and the other 3 ones,especially under 35 ℃ treatment seedlings grew badly.(2)Net photosynthetic rate (P_n) of leaves and photosynthetic product in leaves and roots were higher obviously under 20 ℃ and 25 ℃ treatments than that under 30 ℃,while P_n decreased seriously under 35 ℃ treatment.(3)POD activity was increased and CAT activity was decreased in the leaves and roots under the treatments of 30 ℃ and 35 ℃.SOD and APX activities in the leaves were increased gradually,while both of them showed a reverse trend in the roots with root-zone temperature rising.(4)Leaf relative electrolyte leakage,malondialdehyde (MDA) content in leaves and roots displayed the lowest under 25 ℃ treatment and the highest under 35 ℃ treatment.Proline and soluble protein contents showed the highest in the leaves and the lowest in the roots when seedlings were cultivated in 35 ℃.The results indicated that 25 ℃ was the most suitable root-zone temperature for cucumber seedlings in this research.As the main osmotic regulation substances,proline and soluble protein contents were decreased in roots,the high root-zone temperature acted directly on,and the changes of antioxidant enzyme activities in leaves and roots resulted in oxidative damage of cell membrane increasing severely under 35 ℃ treatment,causing the growth of the whole seedlings to be restrained seriously.