This　paper　reports　the　mechanism　of　hydrogen　enrichment　in　stabilizing　swirl/bluff-body　CH4/air　lean　premixed　flame.　Large　Eddy　Simulation　(LES)　coupled　with　Thickened　Flame　(TF)　model　was　performed　to　resolve　the　turbulent　reacting　flow.　A　detailed　chemistry　was　used　to　describe　the　oxidization　of　CH4/H2/air　mixtures.　Particle　Image　Velocimetry　(PIV)　and　Planar　Laser-Induced　Fluorescence　of　OH　(OH-PLIF)　simultaneous　measurements　were　conducted　to　obtain　the　velocity　fields　and　flame　structures　respectively.　The　numerical　methods　were　validated　by　experimental　data　and　showing　good　agreements.　Both　the　experimental　and　numerical　results　show　that,　the　flame　brush　attachment　tends　to　leave　the　inner　shear　layer　with　increasing　hydrogen　addition,　which　will　reduce　the　risk　of　flame　lift-off.　The　chemical　analyses　prove　that　the　attachment　of　CH4/air　flame　is　inherently　weak.　On　the　one　hand,　the　CH4/air　flame　is　stabilized　by　the　hot　products　inside　the　recirculation.　On　the　other　hand,　the　burnt　gas　suppresses　the　oxidation　of　H2　and　CO　through　H2　+　OH　=　H　+　H2O　and　CO　+　OH　=　CO2　+　H,　respectively.　Although　the　proportion　of　CH4　decomposition　through　CH4　+　OH　=　CH3　+　H2O　will　be　reduced　by　hydrogen　addition,　the　path　of　CH4　+　H　=　CH3　+　H2　will　be　enhanced　significantly.　Hydrogen　addition　will　not　only　increase　the　overall　reaction　rate,　but　also　change　the　combustion　intensity　at　the　nozzle　exit　from　relatively　weak　to　strong,　which　is　also　important　for　flame　stabilization.　The　robust　flame　attachment　obtained　by　hydrogen　addition　can　attributed　to　the　enhanced　reactions　of　H2　+　OH　=　H　+　H2O　and　CH4　+　H　=　CH3　+　H2.　©　2020　Hydrogen　Energy　Publications　LLC