Abstract: The droplet transfer of hyperbaric GMAW was investigated with high speed camera system and infrared laser backlight. Based onthe experiments within 0.4MPa argon environment, it was found that thedroplet transfer mode would be changed if ambient pressure exceeding critical pressure. In the case of low current, as the ambient pressure increases, droplet transfer mode changes to globular transfer, short-circuiting transfer, and repelled transfer. In the case of high current, droplet transfer mode changes to streaming transfer, short-circuiting and streaming mixed transfer, and repelled transfer with increasing ambient pressure. The transition mechanism of metal transfer mode was explained by the droplet force analysis. The arc and its root are contracted at elevated ambient pressure, which results in the force condition changes and the droplet repelled transfer formation.