Abstract: Taking ‘Jinyou 101’ cucumber as test material, two levels of day/night temperature were designed, which were 35 ℃/25 ℃ and 40 ℃/30 ℃ respectively, and relative humidity design 80%.The duration of temperature and humidity treatment were 3,6,9,12 days.Control was set as day temperature/night temperature 28 ℃/18 ℃,relative humidity 50%.Through the above experiments.The changes of photosynthesis and antioxidant enzyme activities of cucumber under the constant humidity and under the high temperature of 35-40 ℃ for different days were studied, so as to explore the effects of high temperature and high humidity environment on photosynthetic characteristics and protective enzyme activities of cucumber leaves at flowering stage.The results showed that, in the maximum daily temperature 35-40 ℃ ranges and as the temperature increases and the number of treatment days increases, cucumber′s maximum photosynthetic rate(Pn_max),apparent quantum efficiency（AQE）,light saturation point（LSP）,stomatal conductance（Gs）,intercellular CO₂ concentration（Ci） all reduced, and superoxide dismutase activity（SOD）,peroxidase activity（POD）,and catalase activity（CAT） increased briefly after high temperature treatment, and then decreased with the increase of treatment days, while light compensation point（LCP） and stomata limit value（Ls）,malondialdehyde（MDA） increased.After resuming treatment for 14 days, all indexes were close to the values of CK control group.Studies have confirmed that high temperature treatment can inhibit photosynthesis through stoma limiting factors, and also reduce the activity of the enzymatic defense system, lead to a deeper degree of lipid peroxidation of cell membranes.Cucumber leaves can alleviate the damage caused by high temperature heat damage through suitable temperature, but the photosynthetic reaction system and antioxidant protection enzyme activities of cucumber leaves treated at 40 ℃ were more difficult to restore to the CK level.