Laser-induced TIG arc welding is used to weld 1.5-mm dissimilar aluminum alloys 6061-T6 and 5083-O to systematically study the influence of the addition of a laser on the collapse and mechanical properties of welded joints. We find that the welded joints appear inconsistent owing to the difference in chemical compositions and thermophysical properties of the two aluminum alloys used. Compared with traditional arc welding, the addition of a laser can not only effectively reduce the degree of collapse of the welded joint, but also greatly reduce the inconsistent collapse depth ratio of the welded joint. Moreover, the inconsistent collapse of the welded joints shows a decreasing trend with the increasing laser power used for welding. It causes the joint stress to change; therefore, the joint strength first increases and subsequently decreases.