Abstract: In order to verify the influence of energy distribution patterns on the quality of dissimilar aluminum alloy welding, a full domain power modulation (FDPM) laser oscillating welding system was used to conduct butt welding experiments on 6061 and 5052 aluminum alloys. A comparison was made on the effects of traditional laser welding (LW) and two laser oscillating welding modes (constant power-CP, gradient power-GP) on the weld seam, porosity, microstructure, and mechanical properties. The results showed that beam oscillation improved the weld seam formation, with the GP mode having the least surface depression. Under the oscillating mode, the proportion of equiaxed grains in the weld seam was higher than that in laser welding, among which the GP mode weld had the highest equiaxed degree, displaying the highest joint strength and fusion zone hardness. The GP mode reduced the temperature gradient of the molten pool during welding, resulting in the largest undercooling and heterogeneous nucleation rate of the molten pool, thus increasing the proportion of equiaxed grains in the weld seam. The laser oscillating welding altered the energy distribution pattern, lowering the energy peak. The energy density at the center of the weld seam was higher under the GP mode than the CP mode, resulting in better fusion of the weld seam.