AbstractUnderstanding the water‐involved mechanism on metal oxide surface and the dynamic interaction of water with active sites is crucial in solving water poisoning in catalytic reactions. Herein, this work solves this problem by designing the water‐promoted function of metal oxides in the ethanol oxidation reaction. In situ multimodal spectroscopies unveil that the competitive adsorption of water‐dissociated *OH species with O₂ at Sn active sites results in water poisoning and the sluggish proton transfer in CoO‐SnO₂ imparts water‐resistant effect. Carbon material as electron donor and proton transport channel optimizes the Co active sites and expedites the reverse hydrogen spillover from CoO to SnO₂. The water‐promoted function arises from spillover protons facilitating O₂ activation on the SnO₂ surface, leading to crucial *OOH intermediate formation for catalyzing C‐H and C‐C cleavage. Consequently, the tailored CoO‐C‐SnO₂ showcases a remarkable 60‐fold enhancement in ethanol oxidation reaction compared to bare SnO₂ under high‐humidity conditions.