Construction of oxygen evolution electrocatalysts with abundant oxygen defects and large specific surface areas can significantly improve the conversion efficiency of overall water splitting. Herein, we adopt a controlled method to prepare oxygen defect-rich double-layer hierarchical porous Co3O4 arrays on nickel foam (DL-Co3O4/NF) for water splitting. The unique array-like structure, crystallinity, porosity, and chemical states have been carefully investigated through SEM, TEM, XRD, BET, and XPS techniques. The designated DL-Co3O4/NF has oxygen defects of up to 67.7% and a large BET surface area (57.4 m2 g−1). Electrochemical studies show that the catalyst only requires an overpotential of 256 mV to reach 20 mA cm−2, as well as a small Tafel slope of 60.8 mV dec−1, which is far better than all control catalysts. Besides, the catalyst also demonstrates excellent overall water splitting performance in a two-electrode system and good long-term stability, far superior to most previously reported catalysts. Electrocatalytic mechanisms indicate that abundant oxygen vacancies provide more active sites and good conductivity. At the same time, the unique porous arrays facilitate electrolyte transport and gas emissions, thereby synergistically improving OER catalytic performance.