The effect of shielding gas compositions containing various oxygen contents on the weld homogeneity and fluid flow is investigated during CO2 laser and gas metal arc (GMA) hybrid welding process. The results indicate that the shielding gas compositions show significant effect on the homogeneity of weld metal in leading laser. Almost homogeneous distribution of alloying elements can be attained if the oxygen content in the arc shielding gas is more than 2%. In He-Ar shielding, the fluid flow behind keyhole is outward, whereas it is inward as the shielding gas contains greater than or equal to 2% O2. These phenomena are mainly determined by Marangoni flow. The direction of Marangoni flow changes from outward to inward when the oxygen content in the shielding gas is over 2%. It promotes the inward flow of the entire molten pool, resulting in homogeneous distribution of alloying elements in hybrid welds.