For the application of electric cars and hybrid cars, the demand for aluminum to the car body is gradually expanding. The use of laser welding on aluminum alloy has a limitation due to the weld defect as like pore and solidification crack, especially 2XXX, 6XXX, and 7XXX. Recently, a beam oscillation method was suggested using the Galvano mirrors to suppress the formation of solidification cracks, which allows the wide weld beads and controlling the thermal history of welds. Oscillation of the heat source changed the shape of weld beads and solidification morphology. However, the formation of solidification cracking on fillet joint subjected laser beam oscillation is still an unknown field. To obtain the understanding of solidification cracking behavior, laser beam oscillation welding performed under various oscillation width and frequency conditions. The effect of the oscillation parameter on the solidification cracking susceptibility was evaluated. The regression analysis progressed based on the shape of the bead, and the stress-strain field was analyzed using FEM simulation. The penetration depth varied according to the oscillation width and frequency, and the length of solidification cracks was reduced with decreasing of back bead width. Also, the loosen stress field generated at the center of the weld bead where is solidification crack propagation root. From the results, it is verified that solidification cracking can be suppressed using the laser beam oscillation.