Abstract: Galvanized sheet has been widely used in automobile industry. However, there are many porosities in the welds of GMAW (gas metal arc welding). In this paper, the effects of welding process, torch moving angle, gap, shielding gas composition and welding speed on porosities were studied systematically. The internal porosities were observed and statistically analyzed by X-ray radiographic inspection. The results showed that CMT (cold metal transfer) welding was suitable for galvanized sheet and had less porosities because of its low heat input. It was better for porosities by using backward-welding (the welding torch points to the unwelded area), leaving the gap, and adding appropriate amount of CO₂ to the shielding gas. And higher welding speed produced more porosities with smaller size.