As　a　newly　modified　welding　heat　source,　hollow　cathode　centered　negative　pressure　arc　(HCCNPA)　has　obvious　changes　in　arc　morphology　and　pressure　distribution　in　comparison　with　traditional　gas　tungsten　arc　(GTA).　To　better　understand　of　these,　in　this　paper　the　arc　behavior　was　monitored　by　using　a　high-speed　image　processing　system.　And　the　influence　of　the　negative　pressure　in　hollow　cathode　was　evaluated　to　study　arc　pressure　distribution　of　HCCNPA,　the　results　were　compared　with　the　conventional　GTAW　process.　It　was　found　that　the　application　of　negative　pressure　greatly　constrains　the　arc　morphology,　which　comes　from　the　interaction　between　the　negative　pressure　at　the　arc　root　and　the　ambient　atmospheric　pressure　nearby　the　arc.　The　maximum　pressure　of　the　HCCNPA　was　smaller　than　that　of　conventional　GTA.　The　application　of　negative　pressure　decreases　the　effect　of　other　parameters　such　as　current　and　arc　length　on　arc　pressure　distribution.　Though　the　results　showed　that　the　HCCNPA　had　much　lower　arc　pressure　than　the　conventional　GTA,　analyses　on　the　bead　appearance　and　cross　section　provided　that　the　density　of　HCCNPA　energy　was　more　evenly.　(C)　2016　The　Society　of　Manufacturing　Engineers.　Published　by　Elsevier　Ltd.　All　rights　reserved.