Abstract: In order to explore the changes of active components and antioxidant activities of ancient fermented tea (Camellia sinensis) Jiaosu after simulated gastric and intestinal digestion, the contents of total phenols, flavones and procyanidins in ancient fermented tea (Camellia sinensis) Jiaosu were determined by the method of in vitro simulated gastric and intestinal digestion. Meanwhile, the changes in the contents of five catechins in tea Jiaosu was investigated before and after gastric and intestinal digestion, and the changes of antioxidant activity in vitro were further studied. The results showed that the contents of total phenols, total flavonoids, ABTS cationic free radical scavenging ability and reducing power were significantly increased (P<0.05), while the content of procyanidins and DPPH free radical scavenging ability had no significant change (P>0.05). In the simulated intestinal digestion, the total phenol content and ABTS cationic free radical scavenging ability increased significantly (P<0.05), while the total flavone content, DPPH free radical scavenging ability and reducing power had no significant change (P>0.05), while the procyanidin content decreased significantly (P<0.05). The contents of catechins, epigallocatechin, epicatechin and epicatechin gallate decreased by 74.58%, 64.40%, 86.95% and 48.21%, respectively. These results indicated that pepsin and gastric acid could promote the release of antioxidant active substances in the simulated gastrointestinal digestion process of ancient tea leaf enzyme, which had good antioxidant activity and was expected to be applied in the development of antioxidant products.