We have separately studied the chlorine evolution reaction (CER) activity of tetrahedral Co2+(CoTd) and octahedral Co3+(CoOh) in spinel Co3O4to demonstrate the geometrical site dependence via an ion-substitution strategy, unveiling that the CoOhsite acts as the main active site for CER. Guided by these findings, the electronic structure of active CoOhsite at the atomic level was accurately regulated to boost electrocatalytic CER.