Abstract: By using one bud two leaves of‘Taiyuan big leaf’species in the summer as materials, the dynamic activity changes of polyphenol oxidase, peroxidase andβ -glycosidase in processing black tea and the effect of water moisture of processing leaves on the enzyme was studied in order to provide reference for processing high incense and high theaflavins black tea. The results showed that with the extension of withering time, the activity of the three enzymes increased differently, after 14 hours withering, polyphenol oxidase activity increased 2.9 times, peroxidase activity increased 3.5 times, andβ -glycosidase activity increased 2.1 times. In rolling, fermentation, drying process, the activity of three kind enzymes decreased differently. According to the results, it could be inferred thatβ -glycosidase affected aroma quality of black tea mainly in the process of fermentation and early withering, polyphenol oxidase, peroxidase affected the taste quality of black tea mainly in the process of fermentation. According to the degree of activity change the three kind enzyme and the condition of water loss in the withering leaves, the appropriate criteria black tea processing could be determined, and the appropriate criteria of fermentation also could be determined according to the ratio changes of polyphenol oxidase and peroxidase.