Abstract: To improve the quality of summer-autumn tea, the fermentation of summer-autumn tea was investigated by using Eurotium cristatum. The contents of tea polyphenols, total free amino acids, total flavonoids, water leachate, and sensory scores of summer-autumn tea were used as the indicators for the one-way experiment, and four factors and three levels were selected for orthogonal experiments to optimize the fermentation process. The volatile compounds of fermented summer-autumn tea under the optimal process were analyzed by gas chromatography-mass spectrometry (GC-MS) technology. The results showed that the optimal fermentation process was 30% water content, 15% inoculum of Eurotium cristatum, fermentation time of 9 d, and fermentation temperature of 30 ℃, and the water leachate content of summer-autumn tea processed under these conditions was significantly increased by 22.51% (P<0.05), the tea polyphenol content was significantly decreased by 27.71% (P<0.05), and the total flavonoid content was significantly decreased by 6.41% (P<0.01), free amino acids did not change significantly, and the sensory score was significantly improved by 10.33 points (P<0.01). In addition, the total amount of flavor compounds was elevated by 296.76% after fermentation, and the content of linalool, linalool oxide I, α-Terpineol, methyl salicylate, and phenethyl acetate substances increased especially significantly throughout the fermentation process, which brought rich fruity and floral aroma to the summer-autumn tea. Thus, the overall quality of summer-autumn tea improved after fermentation treatment.