The invention discloses a laser welding method for a steel/aluminum dissimilar material. According to the laser welding method, an Al2O3 oxidation layer on the surface of an aluminum alloy does not need to be removed, and a Ni/B powder mixture is prearranged on the surface of the aluminum alloy, wherein the mass percentage of B powder ranges from 5% to 15%; laser welding is conducted in the atmosphere of inert gas mixed with a CO2/O2 gas mixture or air, so that the metallurgical reaction in a molten pool is improved through Ni in the Ni/B powder mixture, occurrence of the Fe-Al metallurgical reaction is effectively hindered, and a Fe-Al intermetallic compound at an interface of a welding joint is inhibited from being separated; the B powder is molten and enters the welding molten pool, sothat toughness of an Al-Ni intermetallic compound generated after the Ni is added is improved; either or both of O2 or CO2 are adopted to be mixed with the inert gas, or welding is conducted directlyin a pure air environment, so that the oxygen partial pressure of the welding molten pool is increased, and an element Al and an element O entering the molten pool are combined to form Al2O3 which does not affect the toughness of the welding joint; the thickness of the Fe-Al intermetallic compound at the interface is reduced, and strengthening and toughening of the steel/aluminum dissimilar welding joint are achieved; and the high-quality laser welding joint is obtained.