The main challenges hindering the practical application of seawater electrolysis are the substantial energy input for sluggish oxygen evolution reaction (OER) and anode corrosion by chlorine oxidation reaction (COR). Here we report a simple but reliable strategy of coupling seawater electrolysis with formaldehyde oxidation reaction (FOR) to achieve energy-saving and COR-free dual hydrogen production. For the anode FOR, the onset potential is cut to near -0.2 V vs. the reversible hydrogen electrode (RHE) much lower than the theoretical potential of OER (1.23 V vs. RHE), and the Faradaic efficiencies of both hydrogen and high-value formate products achieve nearly 100 %. In a two-electrode electrolyzer at 100 mA cm−2, the cell voltage of our integrated system is 1.75 V lower than that of the conventional seawater electrolysis, leading to a 66 % reduction in electricity consumption. Moreover, benefiting from the ultra-low reaction potential, the harmful COR is fundamentally avoided. This work opens up a new way to efficiently and stably convert sea resources into hydrogen fuel while also achieving chemical upgrades. Coupling seawater electrolysis with formaldehyde oxidation reaction (FOR) was a simple but reliable strategy to achieve energy-saving and COR-free dual hydrogen production. With Cu/CF/O as the catalyst, this coupled strategy offers a notable economic advantage by reducing 66 % energy consumption for hydrogen production at 100 mA cm−2 and meanwhile enables upgrading formaldehyde to valuable formate products. Display omitted