We　use　density　functional　theory　to　evaluate　the　metals　adsorption　on　the　surface　of　Gallium　Nitride　(GaN)　nanowire　(NW)　and　propose　a　model　to　explore　H-2　sensing　enhancement　mechanism　of　metal-functionalized　GaN　nanowire　in　theory.　The　adsorption　energy　is　negative　when　the　metal　atoms　move　closed　to　the　surface　of　GaN　NWs,　which　reflect　the　feature　of　exothermic　reaction.　Moreover,　the　simulation　indicate　the　metal-functionalized　GaN　have　much　stronger　sensing　to　H-2　by　forming　chemisorption　between　H-2　molecules　and　metal　atoms　on　the　surface,　rather　than　the　conventional　van　der　Waals　forces　between　H-2　molecules　and　the　pure　GaN　surface.　The　latter　can　only　lead　to　a　poor　response　to　H-2　since　the　weak　interactions.　Comparing　with　Au,　Ag　and　Cu-functionalized　surface,　H-2　molecules　are　adsorbed　at　N-functionalized　surface,　with　the　lowest　adsorption　energy,　which　indicate　it　is　expect　to　be　the　most　suitable　for　H-2　detection.　It　should　be　originated　from　the　largest　band　gap　change　and　most　significantly　surface　charge　reconstruction　of　Pt-functionalized　surface.　Our　results　present　an　enhancement　mechanism　of　gas　sensing　from　the　reduction　of　the　surface　potential　by　the　metals　effect,　which　can　be　applied　to　design　and　advance　gas-sensing　materials.