A large number of highly active Ru‐based electrocatalysts have been reported for the hydrogen evolution reaction (HER). The utilization of synergistic effects for promoting HER performance remains inadequate, especially for corresponding potential‐driven reactive sites at the atomic level. Herein, a Co‐substituted RuRu2P structure is employed as a model system to reveal the synergistic effect on Ru‐based electrocatalysts and to realize the potential‐driven reactive sites during the HER. Optimized RuRu2P @ Co0.6 exhibits a superior catalytic performance in alkaline electrolytes, achieving a low overpotential of 9 mV at a current density of 10 mA cm–2. To precisely describe the geometrical nature of surface moiety of Co(µ‐O)2Ru, an indicator (β) is established to quantify the strain of Co(µ‐O)2Ru moieties through calculating the LCoL (L = P or O) angles through employing in situ X‐ray absorption spectroscopy. Both bond strain and corresponding metal‐metal distance of CoRu in Co(µ‐O)2Ru moiety can significantly affect the structural tolerance and facilitate the coupling of adsorbed hydrogen atoms during HER. It is believed that the perspective raised in the present work will provide a new avenue to the design of highly active HER catalysts at the atomic scale. An indicator (β) is established to quantify the strain of Co(μ‐O)2Ru moieties by calculating the LCoL (L = P or O) angles by employing in situ X‐ray absorption spectroscopy. The bond strain of CoRu in Co(μ‐O)2Ru moiety can significantly affect the structural tolerance and facilitate the coupling of adsorbed hydrogen atoms during the hydrogen evolution reaction.