The invention discloses a method for improving the strength of an aluminum-steel dissimilar metal laser fusion welding-brazing lap joint, and relates to the field of metal laser welding. The method comprises the following steps: step 1, cleaning oil stains on the surface of an aluminum alloy, and removing an oxide film on the surface of the aluminum alloy; 2, performing aluminum-steel dissimilar joint lap welding by adopting double laser beams, with the main laser beam being irradiated to an aluminum plate and the second laser beam being irradiated to a steel plate; 3, completely acting the energy of the main laser beam on the aluminum plate to melt the base metal, and freely spreading the molten aluminum base metal on the surface of the steel base metal to form a fusion welding-brazing joint; and 4, acting the second laser beam on the surface of the steel plate, heating edge molten aluminum spread on the surface of the steel plate base metal so that the molten aluminum and the steel plate form an intermetallic compound layer again. The second laser beam which is additionally arranged directly acts on the surface of the steel plate, and the technical effect of improving the performance of a welding joint is achieved.