Covalent organic nanosheets can be applied potentially to solar-to-hydrogen fuel conversion because of their long-range ordered structure and predictable regulation. Additionally, minor progress has been made in the precise synthesis of copper-loaded composite catalysts at the atomic level. Hence, we synthesized hybrid Cu@TpTG-iCON materials by anchoring copper(II) ions into the evenly dispersed tridentate chelation sites of the TpTG-iCON precursor, which maximized the exposure of active sites during the catalytic reaction. Taking advantage of the well-defined structural configuration and nanosheet morphology, the heterogeneous Cu@TpTGiCON catalyst exhibited an excellent hydrogen evolution reaction (HER) rate and significant stability in a ternary photocatalytic system. The atomic-level coordination modulation strategy in the covalent organic nanosheet matrix successfully demonstrated here has made possible the synthesis of other non-precious metal-based hybrid materials, indicating a step forward in the generation of a recyclable and efficient HER catalyst.