Abstract: Based on the high-speed video system and electrical signals analyzing in synchronous, the electrical signals and the photographs of molten droplet under certain welding parameters was collected, the unstable phenomenon of welding process in pulsed MIG welding was studied.It was observed that the unstable welding process of the pulsedMIG welding presented various forms of droplet transfer, the shape and size of molten drop were diverse, the barycenter of melting drop was unstable, droplet exploding brought spatter and the weld pool oscillation.Based on the observation and analysis of the unstable phenomenon of the welding process, it is pointed out that the random variation of melting energy of electrode tip and the forces exerted on the droplet are the vital reasons of the random variation of the drop shape and size.The study on the unstable phenomena of pulsedMIG welding process is helpful to the control of welding technical performance.