Single wire high-current GMAW welding methods with steady metal transfer processes has irreplaceable advan- tages over other high-efficiency GMAW welding methods． Based on the high-speed photography and electric signals se- lecting technology in metal transfer process of GMAW，the differences between MIG and MAG welding were discussed， and the impacts of current or shielding gas constitution on transfer frequency were highlighted． The results indicate that metal transfer style of high-current MIG welding is rotating spray transfer，and the rotating frequency of MIG welding de- crease at first and then increase with the increase of welding current; while in the MAG welding，it becomes a mixing rotating and swing transfer style，and the rotating frequency or swing frequency increases when the flow beam contacts with the weld pool in high current condition． In addition，the external magnetic field can change the rotation direction of large current GMAW flow beam and arc，and reduce the rotation angle． This discovery provides a new idea for the research and development of high efficiency GMAW welding process with single wire over 400A．