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.