Abstract: "8"-shaped oscillating-laser scanning was adopted in GMAW (gas metal arc welding) process to modify the weld pool flow pattern and its temperature field, and thus improve the weld bead formation. Bead-on-plate welding experiments were conducted on 6061 aluminum alloy plates. The effects of major laser scanning parameters, such as the laser-wire distance, laser power and the oscillation amplitude, were experimentally analyzed. A high-speed camera was used to capture the process of laser scanning and the weld pool. Experimental results indicated that oscillating laser scanning could effectively suppress weld bead formation defects; optimal weld formation was obtained when applying oscillating-laser scanning across the middle part of the molten pool. Oscillating-laser scanning reduced the temperature gradients of the weld pool. The laser recoil force could drive the molten pool flow actively, and thus promote the liquid metal spreading and effectively suppress irregularities in bead formation while reducing internal porosity and crack defects. Furthermore, the bead width could be adjusted within a certain range by adjusting the laser scanning amplitude.