The formaldehyde oxidation reaction (FOR) on a Cu-based electrocatalyst enables hydrogen (H₂) at the anode in OH⁻ solution, facilitating a bipolar H₂ production system at ultra-low electrolysis voltage. However, the specific impact of *OH adsorption on the Cu surface regarding the FOR has been rarely investigated. Herein, the strong *OH adsorption Cu (S-OH Cu) electrode, which exhibits high activity and excellent stability of FOR, is developed to investigate the specific impact of *OH adsorption on the Cu surface during the FOR process. Impressively, the increased *OH adsorption on the Cu electrode, typically regarded as a poisoning effect that diminishes inherent FOR activity by reducing the adsorption of intermediate reactants, is firstly revealed as an OH-induced favorable reconstruction effect that significantly improves FOR stability. Specifically, the dual functions of OH-induced favoring reconstruction include accelerating the phase transition of the Cu(0)/Cu(I) redox cycle to refresh the active site and optimizing surface reconstruction to preferentially generate Cu(220) with stronger adsorption energy for H₂C(OH)O* and lower C−H barrier energy during FOR. This work provides a promising strategy for designing stable Cu electrocatalysts for FOR to produce hydrogen with extremely low energy input.