With　the　help　of　high-speed　camera,　the　fundamental　character　of　high　current　density　MAG　welding　process　with　two　types　of　conventional　shielded　gas　is　analyzed.　The　influence　of　wire　extension　and　shielded　gas　component　on　the　second　critical　current　is　researched.　So　the　mechanics　of　drop　transfer　of　high-current　density　MAG　welding　process　is　disclosed,　which　is　centrifugally　breaking　transfer,　mixed　transfer　and　rotating　short　transfer.　Moreover,　the　reason　of　why　high-current　density　MAG　welding　process　with　the　shielded　gas　of　80%Ar　and　20%　CO2　cannot　be　used　is　found.　The　application　practicability　of　high　effective　welding　for　high-current　density　MAG　welding　process　with　the　shielded　gas　of　98%Ar　and　2%　O2　is　built.