Abstract: 5A06 aluminum alloy lock butt weld was used as the research object. Based on the laser beam oscillating, a laser power (power distribution) which is distributed along the oscillating path was added to achieve the dynamic control of power relative to the path. The fluid dynamics model of laser oscillating welding process was established by the finite element software FLUENT to research the effect mechanism of laser oscillating and power distribution on weld forming. The weld section morphology, molten pool dynamic behavior and porosity formation process were simulated and compared under two processes of equal power and power distribution. The results show that compared with the equal power weld, the better formed weld is obtained by power distribution and has no defects such as undercut and burn through. Due to the characteristics of power distribution, the average flow rate of molten pool is effectively reduced, the steady flow behavior of molten metal is exhibited, further improve the stability of the keyhole, and smaller depth-to-width ratio keyhole is obtained, effectively reduce the porosity of the weld (0.9%).