Previous studies have shown that oolong tea has an effective effect on losing weight. As Dancong tea used in this study is a kind of the oolong tea, we speculated that it could also help to reduce fat. The Dancong tea samples with different storage years were obtained from the same producer, and they were produced by the same processing technology. Their compositions were detected and the inhibition of the tea samples on lipase and α-glucosidase activity in vitro was also measured. At the same time, we have analyzed the correlation of these data. The results demonstrated that there was no significant change in caffeine content between the different tea samples. The contents of tea polyphenol, catechins and free amino acid in Dancong tea stored for years were lower than that of the fresh tea, while the contents of aqueous extract, total soluble sugars, gallic acid and theaflavin in Dancong tea stored for years were higher than the fresh tea. Moreover, there was a significant negative correlation between catechin content and theaflavins content, which further proves that TF is the product of catechin oxidation. The experiments in vitro indicated that Dancong tea is able to inhibit lipase activity and α-glucosidase activity. The inhibition of Dancong tea in 1996 on lipase activity was the highest at 43.01%, while it’s the lowest in 2016 at 26.98%. After correlation analyses, it was speculated that gallic acid in tea might be the main effective component of inhibiting lipase activity and reducing weight. On the other hand, the inhibition on α-glucosidase activity was highest in 2016 at 94.48%, while it’s the lowest in 2006 at 89.04%. the correlation analyses showed that caffeine could be the main biological active component to reduce blood sugar. The results provide a theoretical basis for the further development and value-added utilization of single cluster tea.