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Based on the artificial environmental control experiments designed with different low temperatures (5, 7, 9, 11, 25 ℃) as a control experiment (CK), the photosynthesis characteristics, fluorescence parameters, and antioxidant enzyme activity of cucumbers （Cucumis sativus 〖WTBZ〗L. cv. 〖WTBZ〗Jingyou 35） leaves were investigated in 2011 It aimed at determining the low temperature meteorological disaster index of greenhouse cucumbers. Results show that: the maximum photosynthesis rate of cucumber leaves reduced with the increasing low temperature stress；with the prolonging and aggravation of low temperature stress, the light compensation point of cucumbers rose and the light saturation point reduced；under the low temperature treatment of 5, 7, 9 ℃, with the prolonging of the stress,the maximal efficiency of PSⅡ photochemistry of cucumbers and photochemical quenching decreased, while the tendency of non photochemical quenching was opposite to photochemical quenching; with the decreasing treatment temperature, the hyperoxide mutase activity in cucumber leaves increased first and then decreased; the peroxidase activity reached the highest after the 24 h treatment at 9 ℃; as a result of reducing temperature, the catalase activity increased; affected by low temperature stress, malondialdehyde content was greater than that of the control, and with the increasing stress level, it rose first, then descended slightly. The low temperature meteorological disaster index is established, which can be divided into 4 levels: mild, moderate, severe, and very severe, can provide a scientific basis for agro meteorological services.