Controllably　breaking　the　activity-selectivity　trade-offs　in　the　electrocatalytic　oxygen　reduction　reaction　to　produce　H2O2　has　long　been　a　challenge　in　renewable　energy　technologies.　Herein,　by　assigning　the　activity　and　selectivity　requirements　to　two　independent　single-atom　sites,　we　deliberately　engineered　a　Co-Zn　DAC　for　promising　H2O2　electrosynthesis,　from　which　the　Co　sites　provided　the　activity　response　for　oxygen　reduction,　and　the　Zn　sites　regulated　the　reaction　selectivity　toward　the　2e-　pathway.　Through　multidimensional　in　situ　characterizations,　a　potential-dependent　switching　function　of　the　Zn　sites　was　revealed,　which　made　the　increase　in　H2O2　production　at　various　reaction　stages　controllable.　As　a　result,　efficient　H2O2　selectivity　switching　from　11.1%　in　the　single　Co　atom　catalyst　to　94.8%　in　the　Co-Zn　DAC　was　realized,　with　a　prominent　turnover　frequency　of　2.7　s-1　among　the　reported　H2O2-producing　catalysts.　Notably,　a　similar　effect　was　also　observed　in　M-Zn　DACs　(M　=　Pt,　Ru,　or　Ni),　which　demonstrated　the　universal　switcher　role　of　the　Zn　sites.　The　real-time　catalytic　site　behavior　insights　gained　through　this　integrated　experimental　and　theoretical　study　are　envisioned　to　be　valuable　not　only　for　the　ORR　but　also　for　other　energy　catalysis　reactions　involving　activity-selectivity　trade-off　issues.