Herein, a combined method for planetary ball milling and pyrolysis of g-C3N4/cobalt phthalocyanine mixture to synthesize Co nanoparticles loaded on CN nanosheets (g-C3N4@CoPc-x with different mass ratios x of g-C3N4:CoPc) is proposed. The synthesized catalysts exhibit a unique 3D open sheet-like structure, and the average size of Co particles is 4.45 nm while encouragingly, a small amount of quasi single-atom cobalt (mean particle size 0.5 nm) is also found in the samples. In addition, the mass ratio of g-C3N4 to CoPc presents a significant effect on ORR activity of the samples. Among the samples, g-C3N4@CoPc-3 shows excellent ORR performance with the onset potential of 0.94 V in neutral condition and the half-wave potential of 1.00 V in alkaline condition, both better than Pt/C. Its onset potentials in acidic (0.83 V) and alkaline (1.07 V) conditions are also comparable to Pt/C. In a full pH range (acidic, alkaline, and neutral) electrolyte, the prepared samples catalyze ORR via a direct four-electron reaction pathway, and the C3N4@CoPc-3 reveals high catalytic stability and high anti-alcohol tolerance. Results provide wide feasibility for the synthesis and application of g-C3N4@CoPc-3 in fuel cells.