Abstract: The microstructure of the weld metal (WM), heat affected zone (HAZ) and base metal (BM) was studied and tested for the 130 mm thick scanning laser filler wire welded joint of marine 5A06 aluminum alloy rear wall structure members. Vickers hardness and micro-shear test were used to study the difference in mechanical properties of the joints. The results reveal that the single laser welding seam of 5A06 aluminum alloy is dominated by equiaxed crystals, the filler welds are mainly columnar crystals, the HAZ and BM grains are thicker than WM with rolled fibrous structures. Due to the thermal cycle of welding, the hardness of HAZ is slightly higher than BM, and the shear strength is not much different. The hardness and shear strength of the single laser weld are slightly higher than the filler layer, and the overall weld zone strength is low. On the whole, the BM and HAZ have higher shearing strength, while the plasticity is lower.