With the goal of improving the activity of single-atom catalysts, in-depth investigations were performed to design adjacent single-metal sites to produce a modulation effect by using symmetry breaking as an indicator of tuning the electronic structure. A CoN4-ZnN4/C catalyst composed of adjacent Co and Zn sites anchored on nitrogen-doped graphene was predicted by first-principle calculations to exhibit promising bifunctional electrocatalytic activity for oxygen reduction and evolution reactions with an overpotential of 0.225 and 0.264 V, respectively, which is superior to CoN4/C catalysts and outperforms commercial Pt/C and IrO2 benchmarks. The impressive catalytic activity originates from the remarkable asymmetric deformation and strong pseudo-Jahn-Teller vibronic coupling effect, through which the Zn site acts as a modulator to induce the symmetry-breaking phenomenon and tune the d-band structure and binding strength between key intermediates and the Co site. It provides mechanism-based insight for applying diatomic site catalysts for catalytic reactions and further understanding of the modulation effect.