To investigate the physiological mechanism of exogenous ethanol vapor regulation of senescence of postharvest snap bean, the effects of related-senescence physiological indexes of postharvest snap bean applied ethanol (1.5 mL/kg and 3 mL/kg) vapor was studied with a snap bean (Phaseolus vulgaris L. var.chinensisHort.) cultivar WuChang snap bean, with the treatment of clear water vapor as control, and treated materials were stored at room temperature (23 ℃±1 ℃). The results showed that exogenous ethanol vapor significantly reduced the activity of LOX and PPO in snap bean during the storage, and postponed the increase of MDA content. Furthermore, ethanol vapor delayed the peak of CAT and POD activity, and the activity of SOD was induced, which suppressed the synthesis of O^-₂. These findings indicated that there were the difference between both does of ethanol, and that 1.5 mL/kg ethanol was favorable to the normal metabolism of active oxygen and reduced the level of lipid peroxidation, which suspended the speed of snap bean senescence during the storage.