Endowing noble-metal-free electrocatalysts with superior oxygen evolution reaction (OER) activity is essential in water electrolysis for massive and cost-effective production of hydrogen fuels. Here, we presented Mo-doped Co₃O₄ nanoparticles-coated carbon nanotubes (Mo-Co₃O₄/CNTs), which were fabricated through pyrolysis of CNTs-stringed ZIF-67 with the doping of phosphomolybdic acid. The as-prepared Mo-Co₃O₄/CNTs exhibits high OER activity and strong durability with the onset potential of 1.42 V and almost constant low overpotential of 280 mV at 10 mA cm^-2, which outcompete the benchmark IrO₂ electrocatalyst. The outstanding OER performance is mainly attributed that Mo doping modulates the electronic properties and structures of Co₃O₄, which bring out high proportion of Co²⁺ active sites, large specific surface area, more electrophilic Co ions and favorable interfacial charge transfer. This work highlights the modification effects of high-valence metal ions on the structures of the electrocatalysts for improving OER performance.