Abstract: Aimed at the prominent problem of porosity defects of aluminum alloy laser-MIG hybrid welded joints, the influence rule of laser power, arc current, welding speed, heat source distance and defocusing amount on the porosity distribution, size and quantity were systematically studied. The results indicate that the laser power has little impacts on the porosity when realizing full penetration welding. The porosity content and size both increase with the arc current increasing,and when the arc current is bigger than 150 A, the porosities mainly exist near the fusion line due to big arc pressure. The porosity content increases with the welding speed increasing. When the welding speed increases from 0.72 m/min to 2.4m/min, it increases from 0 % to 6.3 % and the porosities mainly exist in the center of the weld seam. The heat source distance of 3 mm is beneficial to reduce the porosity content, and the negative or zero defocusing amount also could effectively reduce the porosity content.