By　using　the　high　speed　camera,　the　arc　and　drop　transfer　behaviors　of　direct　current　electrode　negative　MAG　welding　process　with　different　protecting　atmospheres　and　different　welding　current　levels　are　researched.　The　formation　reason　of　bright　arc　ball　and　its　influence　on　the　stability　of　MAG　welding　process　are　analyzed.　On　this　basis,　the　process　interval　of　direct　current　electrode　negative　MAG　welding　is　determined.　Also　the　influences　of　wire　polarity　on　wire　melting　coefficient　are　compared.　By　using　80%Ar　plus　2%CO2as　shield　gas,　the　drop　transfer　style　belongs　to　large　drop　repulsion　transfer,　so　the　spatter　is　too　large.　But　when　the　shield　gas　is　98%Ar　plus　2%O2,　the　stable　drop　transfer　style　can　be　divided　into　dropwise　transfer　with　low　current　and　streaming　transfer　with　large　current.　For　the　former　one,　with　the　increase　of　welding　current,　the　droplet　dimension　reduces　and　the　drop　transfer　frequency　increases.　For　the　latter　one,　the　arc　is　divided　into　two　parts　in　series.　Both　the　moving　domain　of　the　bright　arc　ball　and　the　stability　of　the　welding　process　can　be　controlled　by　adjustment　of　arc　voltage.　©　2010　Journal　of　Mechanical　Engineering.