Abstract: Based on the Design-Expert V8, the experiments of autogenous laser welding for 3 mm-thick 5A90 aluminum-lithium alloys were implemented. The effects of shielding gas on porosity were investigated. The plots of pore count as a function of side-blowing angle and gas flow rate fitted well as its mathematical model, and the shielding gas parameters were optimized. The results show that the shielding gas can suppress the porosity well, and the gas flow rate is a significant factor, while the side-blowing angle and interaction are not significant. With the increase of gas flow rate, the pore count increased at first then decreased. A minimum value is reached in the range of 5~7 L/min while the optimal blowing angle is in the range of 20~30. The optimal response model for pore count is cubic, and the model has been inspected by validation tests in which the error range is smaller than 10%. The gas flow rate, blowing angle in the ranges of 3~9 L/min, 15~52 respectively are identified as the optimal parameters for grade Ⅰ weld seam.