Spinel　cobalt　oxide　(Co3O4),　consisting　of　tetrahedral　Co2+　(CoTd)　and　octahedral　Co3+　(CoOh),　is　considered　as　promising　earth-abundant　electrocatalyst　for　chlorine　evolution　reaction　(CER).　Identifying　the　catalytic　contribution　of　geometric　Co　site　in　the　electrocatalytic　CER　plays　a　pivotal　role　to　precisely　modulate　electronic　configuration　of　active　Co　sites　to　boost　CER.　Herein,　combining　density　functional　theory　calculations　and　experiment　results　assisted　with　operando　analysis,　we　found　that　the　CoOh　site　acts　as　the　main　active　site　for　CER　in　spinel　Co3O4,　which　shows　better　Cl−　adsorption　and　more　moderate　intermediate　adsorption　toward　CER　than　CoTd　site,　and　does　not　undergo　redox　transition　under　CER　condition　at　applied　potentials.　Guided　by　above　findings,　the　oxygen　vacancies　were　further　introduced　into　the　Co3O4　to　precisely　manipulate　the　electronic　configuration　of　CoOh　to　boost　Cl−　adsorption　and　optimize　the　reaction　path　of　CER　and　thus　to　enhance　the　intrinsic　CER　activity　significantly.　Our　work　figures　out　the　importance　of　geometric　configuration　dependent　CER　activity,　shedding　light　on　the　rational　design　of　advanced　electrocatalysts　from　geometric　configuration　optimization　at　the　atomic　level.　©　2023