The development of electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is crucial for sustainable energy and environmental initiatives. This work establishes an atomically-dispersed Ru-based model to investigate the promoting mechanism by the Ru-Integration effect in RuCo bimetallic nanoparticles supported on nitrogen-doped carbon (RuCo@NC). Specially, the Ru content in RuCo@NC plays a vital role for both HER and OER. The optimized catalyst shows an outstanding performance, requiring only 217 and 97 mV overpotential to reach a current density of 10 mA·cm⁻² for OER and HER respectively in alkaline conditions. Combined with advanced characterizations such as spherical aberration-corrected scanning transmission electron microscopy, X-ray absorption spectroscopy, in-situ Raman spectroscopy, and density functional theory calculations, it is found that Ru plays multiple crucial roles: (1) Ru restricts the growth of large Co NPs, while the small-sized Co NPs facilitate the formation of carbon nanotubes, which significantly enhances the mass/electron transfer; (2) Ru not only tunes the surface properties of Co but also acts as an active site for HER. As a result, when using RuCo@NC as an overall water splitting catalyst, it only needs a potential of 1.62 V to reach a current density of 100 mA·cm⁻². This work offers valuable insights into designing Ru-based electrocatalysts for water splitting.