In the stable system Co 2+-H_2O_2 which can produce hydroxyl radical,bromopyrogallol red is added to determine the absorbance change by spectrophotometry. The scavenging effect of lilium extraction on hydroxyl radical is also studied. By comparing the scavenging effect of lilium extraction with that of ordinary antioxidants,the effect of this method is concluded.The result shows that lilium extraction has a good scavenging effect on hydroxyl radical.