Abstract: In this paper, the chemical components and in vitro antioxidant activities of Camellia sinensis, a large-leaf species in Yunnan were studied. The main biochemical indicators of 13 Yunnan large-leaf tea tree flowers and 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging ability, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) free radical scavenging capacity, total antioxidant capacity (TAC), hydroxyl radical (·OH) scavenging capacity, superoxide anion scavenging capacity, five kinds of in vitro antioxidant indexes were measured. The correlation between the main biochemical components and in vitro antioxidant indexes was analyzed. The results showed that the contents of tea tree flower water extract, tea polyphenols and amino acids were 41.22%~63.73%, 7.74%~13.56%, 1.61%~5.91%, respectively. The contents of caffeine and flavonoids were 4.98~8.46, 4.21~8.63 mg/g, respectively. Each sample showed a certain difference. There were significant differences in the in vitro antioxidant capacity of different tea tree flower samples (P<0.05). Among them, the ancient tea tree flowers of Dijie, Bulang Mountain, and Bingdao showed good antioxidant activities, while the ancient tea flowers of Yangta white tea were the weakest. The antioxidant activity of tea tree flowers in vitro was correlated with biochemical indicators, tea polyphenols were significantly correlated with total antioxidant capacity (P<0.01), epigallocatechin gallate (EGCG), epicatechin gallate Epicatechin gallate (ECG) was significantly correlated with total antioxidant capacity (P<0.05), and the results could be used as an important indicator to predict the antioxidant activity of tea flowers.