For developing high performance zinc-air battery, an integrated air electrode with rational design of the catalyst layer and gas diffusion layer (GDL) was proposed using a facile and scalable method, in which an in-situ grown Co3O4 nanosheets was employed to tailor the pore sizes and properties of the GDL with efficient oxygen-transfer channels as well as more triple-phase boundaries. The Co3O4 nanosheets were directly grown both on the surface of nickel foam and the large pores of GDL. Therefore, this approach avoided blocking active sites due to a binder, and enabled tailoring of the architecture and properties of the GDL, resulting in more exposed active sites, fast oxygen transport capability, and abundant triple-phase boundaries. Remarkably, benefitting from their unique architecture, the Co3O4/Ni/GDL electrodes exhibited high activity toward both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Application of the Co3O4/Ni/GDL electrodes as bifunctional electrodes for zinc–air batteries resulted in an ultrahigh capacity of 806 mAh/gZn, high maximum power density of 162 mW/cm2, and superior cycling stability over 425 h at 10 mA/cm2 with a high energy efficiency of 68%. These properties were much better than those of Pt/C-based electrodes. Furthermore, the Co3O4/Ni/GDL-based flexible zinc-air battery also exhibited high mechanical flexibility and stability. Our findings thus open up a path for the design of highly efficient integrated air electrodes for metal-air batteries.