The　oxygen　reduction　reaction　(ORR)　catalyzed　by　transition-metal　single-atom　catalysts　(SACs)　is　promising　for　practical　applications　in　energy-conversion　devices,　but　great　challenges　still　remain　due　to　the　sluggish　kinetics　of　O═O　cleavage.　Herein,　a　kind　of　high-density　iron　network-like　sites　catalysts　are　constructed　with　optimized　intermetallic　distances　on　an　amino-functionalized　carbon　matrix　(Fe-HDNSs).　Quasi-in　situ　soft　X-ray　absorption　spectroscopy　and　in　situ　synchrotron　infrared　characterizations　demonstrate　that　the　optimized　intermetallic　distances　in　Fe-HDNSs　can　in　situ　activate　the　molecular　oxygen　by　fast　electron　compensation　through　the　hybridized　Fe　3d‒O　2p,　which　efficiently　facilitates　the　cleavage　of　the　O═O　bond　to　*O　species　and　highly　suppresses　the　side　reactions　for　an　accelerated　kinetics　of　the　4e−　ORR.　As　a　result,　the　well-designed　Fe-HDNSs　catalysts　exhibit　superior　performances　with　a　half-wave　potential　of　0.89 V　versus　reversible　hydrogen　electrode　(RHE) and　a　kinetic　current　density　of　72 mA cm−2@0.80 V　versus　RHE,　exceeding　most　of　the　noble-metal-free　ORR　catalysts.　This　work　offers　some　new　insights　into　the　understanding　of　4e−　ORR　kinetics　and　reaction　pathways　to　boost　electrochemical　performances　of　SACs.　©　2024　Wiley-VCH　GmbH.