Hydrogen　energy　is　a　resuscitated　clean　energy　source　and　its　sensitive　detection　in　air　is　crucial　due　to　its　very　low　explosive　limit.　Metal　oxide　decorated　with　noble　metal　nanoparticles　has　been　used　for　the　enhancement　of　gas　detection　and　exhibits　superior　sensitivity.　Understanding　the　intrinsic　mechanism　of　the　detection　and　the　enhancement　mechanism　is　thus　becoming　a　fundamental　issue　for　the　further　development　of　novel　metal/oxide　compound　gas-sensing　materials.　However,　the　correlation　between　the　microstructural　evolution,　the　charge　transport　and　the　complex　sensing　process　has　not　yet　been　directly　revealed　and　its　atomic　mechanism　is　still　debatable.　In　this　study,　an　Au/WO(2.7)compound　was　synthesized　and　exhibited　a　strongly　enhanced　gas　sensitivity　to　many　reductive　gases,　especially　H-2.　Aberration-corrected　environmental　transmission　electron　microscopy　was　used　to　investigate　the　atomic-scale　microstructural　evolutionin　situduring　the　reaction　between　H-2　and　Au/WO2.7　compound.　Swing　and　sintering　processes　of　the　Au　particles　on　the　WO2.7　surface　were　observed　under　heating　and　gaseous　environments,　and　no　injection　of　hydrogen　atoms　was　suggested.　First　principle　calculations　verified　the　swing　and　sintering　processes,　and　they　can　be　explained　by　the　enhancement　of　H-2　sensitivity.