<p>This study systematically examines the impact of shielding gas composition (pure Ar and pure CO₂) on the laser welding of galvanized high-strength steel. The analysis focuses on the dynamic behavior of surface plasma plumes, weld morphology, mechanical properties of joints, and metallurgical interactions between the shielding gas and zinc coating within the molten pool. Research results indicate that the surface plasma plume under CO₂ shielding gas exhibits a mushroom cloud-like morphology, whereas under Ar shielding gas it appears as a clustered form. The area of the plasma plume generated with CO₂ shielding gas occupies approximately 66% of that produced under Ar shielding gas. Welded joints produced under CO₂ shielding gas are prone to the formation of black particulate matter on the surface, along with a higher number of spatter particles. The primary issue arises from the influence of the zinc coating. Zinc vapor undergoes intense evaporation at relatively low temperatures, and its subsequent volumetric expansion into the keyhole or molten pool disrupts the stability of molten pool flow. In terms of microhardness, the softening degrees of the welded joints under Ar and CO₂ shielding gases decreased by 14.24 and 19.97%, respectively, with the softened areas concentrated in the mixed-grained zone of the heat-affected zone. In terms of tensile and formability properties, the welded joints produced with CO₂ shielding gas exhibit superior performance compared to those with Ar shielding gas. When weld surface appearance is not a primary consideration, CO₂ shielding gas may be prioritized due to its advantages in cost-effectiveness and specific mechanical performance.</p>