Oxygen　evolution　reaction　(OER)　is　a　critical　process　in　electrocatalytic　water　splitting.　However,　the　development　of　low-cost,　highly　efficient　OER　electrocatalysts　by　a　simple　method　that　can　be　used　for　industrial　application　on　a　large　scale　is　still　a　huge　challenge.　Recently,　high　entropy　alloy　(HEA)　has　acquired　extensive　attention,　which　may　provide　answers　to　the　current　dilemma.　Here,　we　report　bulk　Fe50Mn30Co10Cr10,　which　is　prepared　by　3D　printing　on　a　large　scale,　as　electrocatalyst　for　OER　with　high　catalytic　performance.　Especially,　an　easy　approach,　corrosion　engineering,　is　adopted　for　the　first　time　to　build　an　active　layer　of　honeycomb　nanostructures　on　its　surface,　leading　to　ultrahigh　OER　performance　with　an　overpotential　of　247　mV　to　achieve　a　current　density　of　10　mA　cm−2,　a　low　Tafel　slope　of　63　mV　dec−1,　and　excellent　stability　up　to　60　h　at　100　mA　cm−2　in　1　M　KOH.　The　excellent　catalytic　activity　mainly　originates　from:　(1)　the　binder-free　self-supported　honeycomb　nanostructures　and　multi-component　hydroxides,　which　improve　intrinsic　catalytic　activity,　provide　rich　active　sites,　and　reduce　interfacial　resistance;　and　(2)　the　diverse　valence　states　for　multiple　active　sites　to　enhance　the　OER　kinetics.　Our　findings　show　that　corrosion　engineering　is　a　novel　strategy　to　improve　the　bulk　HEA　catalytic　performance.　We　expect　that　this　work　would　open　up　a　new　avenue　to　fabricate　large-scale　HEA　electrocatalysts　by　3D　printing　and　corrosion　engineering　for　industrial　applications.　©　2021