Practically　investigate　water　removal　and　cell　performance　for　PEMFCs　under　low　gravity　circumstance　is　an　urgent　task,　especially　as　a　promising　power　supply　unit　applied　to　space　engineering.　PEMFC　with　an　in-situ　optical　flow　field　was　used　to　explicate　two-phase　flow　and　water　removal　inside　cathode　flow　field　from　terrestrial　gravity　to　microgravity.　The　cell　was　tested　in　the　vertical　and　horizontal　flow　channel　orientations.　A　3.6　s　short-time　micro-gravity　circumstance　was　provided　by　National　Micro　gravity　Laboratory.　Results　show　that　gravitational　level　has　an　essential　influence　on　gas-liquid　two-phase　flow　characteristics　for　PEMFC　with　different　configurations.　The　cell　placed　in　different　channel　orientations　also　shows　distinguished　operating　behavior　because　of　the　complicated　impact　of　the　changed　gravity　and　configuration.　Under　the　operating　condition　of　a　vertical　flow　channel　orientation,　accumulated　water　and　droplets　in　terrestrial　are　pushed　by　oxygen　flow　to　continuous　removal　toward　the　outlet　of　the　fuel　cell　to　alleviate　water　flooding,　and　the　cell　performance　is　slightly　enhanced　in　a　3.6　s　micro-gravity　circumstance.　Operating　in　a　horizontal　flow　channel　orientation,　the　generated　water　throughout　the　micro-gravity　circumstance　duration　is　not　prone　to　move　and　flood　flow　channels　in　micro-gravity,　meanwhile　the　cell　performance　is　slightly　deteriorated.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.