Benzoic acid with weak fluorescence may react on *OH, and then products with intense fluorescence are made. Extractives of Chinese traditional medicine may eliminate *OH in solution, and reduce the amounts of the products. Then, the increased level of fluorescence of the products in solution will be lowered. Based on this principle, a novel catalysis kinetics fluorimetry system for the determination of eliminating ratio of Chinese traditional medicine for *OH was developed. When the concentration of traditional Chinese herbal drugs was 4.0 mg (dry weight) x mL(-1), the eliminating ratios of Viola yedoensis, Atrctylodes chinensis and Paeonia veitchii were 60.8%, 40.1% and 94.3%, respectively. The results obtained by this method are in good agreement with those obtained by spectrophotometry.