By studying absorption spectrum, oxidation velocity of pyrogallic acid reaction system, the effect of pyrogallic acid concentration and buffer pH value on the scavenging rate for superoxide anion free radical coming from reaction system was investigated, and some results were obtained as follows, the wavelength used for the pyrogallic acid reaction system was determined by spectrophotometric method: 319.5 nm. Some parameters of the reaction system were determined as follows: reaction volume: 10 mL, reaction time: 9 min, volume of pyrogallic acid (3 mmol x L(-1)): 0.3 mL, pH value of buffer: 8.2 and oxidation velocity: 0.035. The relation between scavenging rate for superoxide anion free radical and concentration of TBHQ and bamboo leaf extract samples was studied by our method, and IC50 (the value of antioxidant concentration at scavenging half of superoxide anion free radical) was used as the index to evaluate scavenging capacity. IC50 value of TBHQ and most effective samples were as follows: TBHQ (95.01 mg x L(-1)) and M40 (298.69 mg x L(-1)). M40 and other bamboo leaf extract could be used as natural antioxidant.