Abstract: The stability of droplet transfer is crucial for the quality of high current MAG welding. A high-speed camera system and electrical signal acquisition system were used to study the unstable droplet transfer process, arc morphology, and electrical signal of high current MAG. The formation mechanism of unstable droplet transfer was revealed, and the factors affecting the critical current value of unstable droplet transfer in high current MAG were analyzed. The results showed that the droplet transfer in high current MAG welding is an unstable transition mode consisting of swing and mixed transfer. The instability of the liquid cone due to strong electromagnetic force and deviation from the welding wire axis are the direct reasons. The arc rotation/swing frequency varies with the droplet transfer mode and arc shape. Dry elongation is the main factor affecting the critical current value of unstable droplet transfer, and the critical current value significantly decreases with the increase of dry elongation.