The　regulation　of　single-atom　catalyst　(SAC)　through　microenvironment　engineering,　particularly　via　peripheral　species,　has　recently　garnered　significant　attention　in　the　fields　of　materials　science　and　heterogeneous　catalysis.　Nevertheless,　establishing　unambiguous　structure-property　relationships　for　SAC,　especially　concerning　peripheral　effects,　remains　a　significant　challenge.　Herein,　we　propose　a　strategy　for　the　design　of　N-doped　carbon-supported　Fe　SACs　for　CO2　reduction　reaction　(CO2RR).　Density　functional　theory(DFT)　calculations　reveal　that　installing　five-　or　six-membered　ring　in　the　outer　shell　modulates　the　electronic　properties　of　the　inner-shell　coordination　N　species,　altering　their　electron　transfer　capabilities　while　fine-tuning　the　d-p　coupling　between　the　Fe　center　and　adjacent　N　atoms.　Notably,　five-membered　rings　induce　stronger　d-p　coupling　compared　to　their　six-membered　counterparts,　leading　to　a　higher　Fe　valence　state.　This　electronic　modulation　optimizes　the　adsorption　strength　of　key　CO2RR　intermediates　(COOH*　and　CO*),　enhancing　catalytic　performance　for　CO　production. Extensive　experimental　studies　corroborate　these　theoretical　findings.　The　proposed　“outside-in”　design　strategy　can　be　extended　to　Ni　SACs,　offering　new　insights　into　the　exploration　of　highly　efficient　single-atom　centers　through　peripheral　geometric　effects.　©　2025　Wiley-VCH　GmbH.