Hybrid　materials,　integrating　the　merits　of　individual　components,　are　ideal　structures　for　efficient　oxygen　evolution　reaction　(OER).　However,　the　rational　construction　of　hybrid　structures　with　decent　physical/electrochemical　properties　is　yet　challenging.　Herein,　a　promising　OER　electrocatalyst　composed　of　trimetallic　metal-organic　frameworks　supported　over　S/N-doped　carbon　macroporous　fibers　(S/N-CMF@FexCoyNi1-x-y-MOF)　via　a　cation-exchange　strategy　is　delicately　fabricated.　Benefiting　from　the　trimetallic　composition　with　improved　intrinsic　activity,　hollow　S/N-CMF　matrix　facilitating　exposure　of　active　sites,　as　well　as　their　robust　integration,　the　resultant　S/N-CMF@FexCoyNi1-x-y-MOF　electrocatalyst　delivers　outstanding　activity　and　stability　for　alkaline　OER.　Specifically,　it　needs　an　overpotential　of　296　mV　to　reach　the　benchmark　current　density　of　10　mA　cm(-2)　with　a　small　Tafel　slope　of　53.5　mV　dec(-1).　In　combination　with　X-ray　absorption　fine　structure　spectroscopy　and　density　functional　theory　calculations,　the　post-formed　Fe/Co-doped　gamma-NiOOH　during　the　OER　operation　is　revealed　to　account　for　the　high　OER　performance　of　S/N-CMF@FexCoyNi1-x-y-MOF.