A better understanding of the transport mechanism in the metal during a welding process is important for the improvements in the quality and productivity of welding. This project studied the influences of shielding gas compositions on the transport phenomena in the metal domain during gas metal arc welding (GMAW), which include the transient processes of electrode melting; the droplet formation, detachment, transfer and impingement onto the workpiece; and the weld pool dynamics and bead formation. The present study shows that electromagnetic force, which is affected by shielding gas compositions, plays the most significant role in determining the behaviors of metal transfer. For the same welding power input, the increase of He content in the mixture leads to the formation of larger droplets and the decrease of droplet detachment frequency. The predicted phenomena on metal transfer are consistent with the reported experimental observations