As　the　shield　cutter　head　needs　welding　repair　when　it　is　worn,　and　hyperbaric　welding　technique　should　be　used　in　the　case　chamber　cannot　be　opened　for　maintenance　under　normal　pressure.　This　paper　introduced　the　technical　principle　of　cutter-head　maintenance　in　hyperbaric　environment,　presented　the　maintenance　plan　of　air　diving　and　SMAW&MMA　for　the　Beijing　underground　transit　line　project.　The　explosion　combustibility　test　under　compressed　air　was　carried　out　in　view　of　less　study　of　SMAW&MMA　of　underwater　dry-type　hyperbaric　welding　technique,　and　the　test　results　show　that　compressed　air　is　a　good　combustion　improver,　yet　explosion　would　not　occur　if　volume　ratio　of　combustible　concentration　is　less　than　5.6%　when　air　pressure　is　not　more　than　0.6　MPa.　Additionally　a　technological　test　of　SMAW&MMA　and　carbon　arc　gouging　was　conducted　in　air　cushion　chamber　at　pressures　of　0.15　MPa,　0.22　MPa　and　0.3　MPa　respectively,　the　process　of　welding　operation　was　safe　and　successful,　the　quality　of　welded　specimens　met　the　welding　technical　requirements　of　AWD　D3.6M:1999.　This　welding　technique　under　compressed　air　can　be　widely　applied　in　maintenance　of　cutter-head,　which　will　fully　complete　the　tasks　like　rib　plate　cutting,　flush　pipe　cutting,　welding　and　maintenance　work　of　cutting　tools.　©,　2015,　Editorial　Office　of　＇Modern　Tunnelling　Technology＇.　All　right　reserved.