Butt welding-brazing joint between 5A06 aluminum alloy and ST04Z steel sheets was obtained by low power arc-assisted laser welding with preplaced filler powder. The influence of pre-welding gap, filling brazing flux, laser heat input, assistant arc current, heat source center distance and adding welding wire on spreading characteristics of the filler metal was studied by using SEM, Photoshop. The results show that the pre-welding gap less than 0.5 mm and the filling brazing flux on the welds' back were favorable. When the workpiece was not burn through, the weld spreading width was increased with the increase of the laser heat input and assistant arc current. With the increase of the distance to the heat source center, the weld spreading width first increaseed then decreased. Adding wire welding in the molten pool offers better spreadability, continuous and sound weld appearance can be obtained than the condition without wire addition.