Nitrogen　reduction　electrocatalysts　are　highly　attractive　for　catalytic　science.　However,　most　electrocatalysts　are　limited　by　their　low　faradaic　efficiency,　poor　ammonia　yield,　and　tedious　and　costly　catalyst　synthesis　process.　In　this　work,　Fe-based　oxide　composite　nanoparticles　with　steady　chemical　states　are　prepared　by　a　single-step　green　procedure　under　ambient　conditions.　The　resulting　Fe-Fe3O4　demonstrates　remarkable　activity　and　selectivity　for　nitrogen　reduction　reaction　(NRR)　with　the　highest　faradaic　efficiency　of　53.2　+/-　1.8　%　and　NH3　yield　rate　of　24.6　+/-　0.8　mu　g　h(-1)　mg(cat.)(-1)　at　-0.4　V　(vs.　RHE)　in　0.1　m　Na2SO4　electrolyte.　Characterization　experiments　and　theoretical　calculation　reveal　that　Fe-Fe3O4　exhibits　significantly　enhanced　charge　transfer　capability　and　suppresses　the　competitive　HER　process.