Electrochemiluminescence　(ECL)　as　a　light-emitting　process　involves　the　interfacial　charge　transfer　between　the　electrochemically　generated　emitter＇s　intermediate　and　the　coreactant/emitter,　critically　governed　by　the　emitter＇s　electronic　structure　and　exposed　surface　state.　However,　the　relationship　between　the　emitter＇s　exposed　surface　state　and　ECL　performance　remains　unexplored.　Herein,　a　series　of　metal-organic　framework　(MOF)　emitters　is　synthesized　via　controlled　crystal　growth,　achieving　selective　exposure　of　(001),　(100),　and　(110)　facets　characterized　by　micro-electron　diffraction　(MicroED)　on　nanoplate,　nanoblock,　and　nanorod-shaped　MOFs,　respectively.　Compared　to　(001)　facet,　the　(110)　and　(100)　facets　exhibit　19.5　and　2.4-fold　enhancement　of　ECL　intensity,　pronouncing　facet-dependent　ECL　performance.　Notably,　the　(110)　facets　exhibit　1088-fold　ECL　self-amplification　due　to　the　accumulation　of　stabilized　radicals.　Density　functional　theory　calculations　identify　that　the　coreactant　peroxydisulfate＇s　lateral　coordination　with　Zn(II)　on　the　(110)　facet　strengthens　chemisorption,　elongates　the　O─O　bond,　and　promotes　its　cleavage　to　form　SO4•−　radicals,　thereby　facilitating　interfacial　charge　transfer　to　generate　more　excited　states　for　ECL　emission.　The　facet　engineering　provides　a　mechanistic　guideline　for　designing　crystalline　ECL　nanoemitters　and　decoding　the　fundamentals　of　ECL　techniques.　©　2025　Wiley-VCH　GmbH.