Fresh tea leaves of twenty cultivars of tea plants were investigated. The season of harvesting and the methods of plucking were concerned as factors which could affect the enzymic activity of the endogenous polyphenol oxidase(PPO) as well as its isozyme. As a result, three of the tea cultivars were distinctively selected out. In the order of the enzymic activity from high to low, they were Zheng-he White Tea, Fu-yun 6th and Large-leaved Tao-yuan Tea. The fresh tea leaves were mashed, the effectivenesss of enzymic synthesis of theaflavins were observed, meanwhile, instant green tea was considered as an added substrate to promote the yield. The results showed that the one bud and two leaves shoot exhibited high enzymic activity of PPO, the different tea cultivars presented the isozymes of PPO with diversities in three aspects including the number of the isozymes bands, value of retention factor and the darkness of spectral color. Two isozyme bands of PPO appeared in every one of the sampled twenty tea cultivars, with the Rf value of 0.27 and 0.53, each of Zheng-he White Tea, Fu-yun 6th and Large-leaved Tao-yuan Tea possessed five evident isozyme bands, Zheng-he White Tea exhibited the darkest of the spectral color, while it yielded highest theaflavins per unit mashed tea leaves than those of Fu-yun 6th and Large-leaved Tao-yuan Tea produced, EC, EGCG and ECG were the major polyphenols which were involved in the enzymic synthesis; the yield of theaflavins was enormously enhanced by the added substrate of instant green tea, the theaflavins concentration of 212.01 mg/L was gained from the Zheng-he White Tea processing system, which reached the 5.43 times of the yield producing by the fresh tea leaves without the addition of instant green tea substrate.