With cherry tomato’Devil’as the test material, effect of low nocturnal temperature at 5℃, 8℃ and 11℃simulated by climate chambers on the active oxygen metabolism, antioxidant enzyme activity, malondialdehyde（MDA） and soluble protein of tomato leaves were studied, taking nocturnal temperature 15℃ as the control. The results showed that low noctural temperature treatment increased O₂^-. production rate, H₂O₂, malondialdehyde（MDA）contents and soluble protein contents. The activity of SOD and CAT showed a tendency to rise first and then decrease under nocturnal low temperature stress. The activity of SOD was higher than that of the control, but CAT activity was lower than the control at the later stage of treatment. The POD activity increased with the prolongation of treatment time and temperature.