Ruthenium (Ru) has been theoretically considered a viable alkaline hydrogen evolution reaction electrocatalyst due to its fast water dissociation kinetics. However, its strong affinity to the adsorbed hydroxyl (OH_ad) blocks the active sites, resulting in unsatisfactory performance during the practical HER process. Here, we first reported a competitive adsorption strategy for the construction of SnO₂ nanoparticles doped with Ru single-atoms supported on carbon (Ru SAs-SnO₂/C) via atomic galvanic replacement. SnO₂ was introduced to regulate the strong interaction between Ru and OH_ad by the competitive adsorption of OH_ad between Ru and SnO₂, which alleviated the poisoning of Ru sites. As a consequence, the Ru SAs-SnO₂/C exhibited a low overpotential at 10 mA cm⁻² (10 mV) and a low Tafel slope of 25 mV dec⁻¹. This approach provides a new avenue to modulate the adsorption strength of active sites and intermediates, which paves the way for the development of highly active electrocatalysts.