The simple one-step synthesis of face-centered cubic (fcc) Ru and RuO2 co-existing electrocatalysts for excellent overall water splitting through reasonable design and assembly protocols remains a formidable challenge. Herein, fcc Ru-RuO2/C electrocatalyst was successfully synthesized for the first time in one step by wet impregnation method with the help of alkaline solvent. As expected, the overpotential of fcc Ru-RuO2/C at 10 mA cm−2 is 30 mV and 283 mV, respectively, which is better than the 44 mV and 331 mV of commercial Pt/C and RuO2. Theoretical calculations disclose that the superior performance is mainly attributed to fcc Ru and RuO2 nanoparticles cooperating to change the electronic structure and make the adsorption behavior of reaction intermediates much close to the suitable level, thus greatly accelerating the hydrogen evolution kinetics and reducing the energy barrier of oxygen evolution. This work not only highlights the importance of phase engineering, but also elucidates the necessity for obtaining bifunctional catalysts in which metal and oxide co-exist.