Tea is a rich source of bioactive compounds, with catechin recognized as key antioxidants. However, the influence of metal ions on the antioxidant activity of catechin remains further exploration. In this study, the interaction between catechin and Cu was well explored and a mechanism of coordination-activation effect was successfully proposed. It was demonstrated that moderate concentrations of Cu could significantly enhanced the antioxidant capacity of catechin. Structural analyses revealed the formation of coordination complexes between Cu and catechin, which underlay this enhanced antioxidant activity. Additionally, density functional theory calculations indicated that complex formation could reduce the HOMO-LUMO energy gap obviously, thereby contributing to enhanced antioxidant capacity. Our findings offer new insights into the modulation of antioxidant activity by metal ions. This research not only deepens understanding the bioactivity of tea but also suggests potential strategies for optimizing tea-based products, advancing the broader field of antioxidant research.