To address the limited high-value utilization of Dancong summer tea due to its inherently bitter and astringent taste, this study employed it as a raw material with the aim of establishing a polyphenol-enrichment technology, elucidating its bioactivities and key regulatory components, thereby providing a basis for further processing and value addition. The total phenolic content and bioactivities of the extracts were systematically evaluated, leading to the optimization of an enrichment process combining 40% ethanol ultrasonic-assisted extraction with ethyl acetate partitioning. Enzyme inhibition mechanisms were determined via kinetic analysis, and ultra-high-performance liquid chromatography coupled with electrospray ionization time-of-flight tandem mass spectrometry (UHPLC-ESI-TOF-MS/MS) was used to characterize the chemical composition. In addition, correlation analysis was conducted to construct an activity–compound relationship model. The results showed that the optimized process yielded an extract with a total phenolic content of 648.98 mg GAE g?¹, representing a 57.48% increase compared with hot-water extraction. The DPPH and ABTS? radical scavenging activities exhibited IC?? values of 6.71 and 27.69 μg mL?¹, respectively, both superior to vitamin C. The inhibitory activities against α-glucosidase and α-amylase showed IC?? values of 1.65 and 0.40 mg mL?¹, respectively, outperforming acarbose. Both enzyme inhibition modes were identified as non-competitive mixed inhibition. Composition quantification and correlation analysis confirmed that catechins, including epigallocatechin gallate (EGCG), catechin (C) and epigallocatechin (EGC), were the key bioactive constituents responsible for antioxidant and hypoglycaemic activities. Overall, the developed extraction strategy is efficient and feasible, clarifying both the functional advantages and the core bioactive basis of Dancong summer tea. These findings expand its potential applications in functional foods and provide a new pathway for its high-value utilization.