The development of the hydrogen evolution reaction (HER) in alkaline electrolyte is highly desirable but is hindered by sluggish water dissociation and the high cost of Pt–based catalysts. In this study, a facile pyrolyzation method is proposed for synthesizing the Ru nanoclusters (NCs) anchored on B/N–doped graphene (BNG) (denoted as Ru NCs/BNG). During the pyrolyzation, boron was doped into graphene and facilitated the formation of ultra−small Ru NCs with a diameter of 0.5–1 nm. The electronic interaction between B and Ru NCs accelerated the cleavage of H–OH, altering the HER mechanism and lowering the activation energy of H₂ formation, endowing Ru NCs/BNG with excellent alkaline HER activity, even surpassing that of Pt/C. This study reveals the importance of water dissociation barriers for alkaline HER activity and provides a new strategy for improving the HER catalytic activity.