Abstract: After the harvesting of broccoli,the contents of toluble protein and ascorbic acid (AsA) together with the activities of superoxjide dismutase (SOD) and lifxjxldase (LOX) decreased constantly; lipid peroxidation increased,causing senescence in the flower buds. The effects of exogenous AsA on deferring the senescence varied with different AsA concentrations and times of treatment. 100mg/L AsA deferred the senescence slightly; 50mg/l AsA didn’t show evident deferring effect;while 200 mg/L and 100mg/L AsA with daily treatment promoted the senescence. The defer-ring effect of lower AsA concentration on the senescence was mainly related to the delay of endogenous AsA degradation and the stimulation of SOD activity. The decrease of LOX activity didn’t play an important role in deferring senescence. The promoting effect of higher AsA concentration on the senescence was probahly related to thedecrease of SOD activity,the promotion of Fenton reaction and the formation of free radical.OH which had stronger oxidizing force.