Abstract: In order to improve the utilization rate of fresh leaves of Tieguanyin tea, Eurotium cristatum was inoculated to Tieguanyin tea for solid-state fermentation, and the changes of chemical composition and antioxidant activity in tea leaves after fermentation were investigated. Results showed that, the ingredient in tea, such as polyphenols, epigallocatechin gallate (EGCG), (−)-epicatechin gallate(ECG), theaflavins, free amino acid, maltose, sucrose and fructose content were significantly lower(P<0.05) after fermentation. In detail, EGCG and ECG decreased by 92.2% and 88.1%, respectively. Flavonoid, (−)-epigallocatechin (EGC), catechin (+C), L-epicatechin (EC), total sugar, glucose, triterpenes, thearubigins and theabrownins content significantly increased(P<0.05), and theabrownins increased by 68.4%. Compared with the control group, the total reducing ability, Fe³⁺ reducing ability, DPPH, ABTS⁺ and hydroxyl radicals scavenging ability of the fermentation group maintained strong ability. The solid fermentation by E. cristatum reduced the amount of tea polyphenols in the leaves, which added a bit of bitterness to the tea, and increased the total sugar, thearubigins, theabrownins, EGC, +C, EC and other components, thus improved the quality of Tieguanyin tea. The study would lay an experimental basis for the effective utilization of fresh Tieguanyin tea leaves.