Dissimilar metal welding of Q235 low carbon steel and 5052 aluminum alloy was carried out by a single/dualbeam laser in a steel-on-aluminum overlap configuration with a copper interlayer. The weld appearance, microstructure, and fracture behavior of the joints made by the single/dual-beam laser welding were investigated comparatively. The results showed that dual-beam laser welding, compared with singlebeam laser welding, had better process stability which made better weld appearance and bigger effective joining width which enhanced tensile capacity. With a copper interlayer, a contact reaction zone appeared between the copper interlayer and aluminum matrix, which enlarged effective joining zone. The microstructures of the welding joint welded by a single/ dual-beam laser were composed of the ligulate fusion zone with Fe-Al interface and the contact reaction brazing zone with Al-Cu interface. The Fe-Al interface mainly consisted of α-Al and Al 2 Cu eutectic structure, FeAl, FeAl 2 , and a certain amount of Al-Cu intermetallics, Fe 2 Al 5 and FeAl 3 . The Al-Cu interface mainly consisted of eutectic phase Al 2 Cu and metastable phase of Al-Cu intermetallics. The tensile property was enhanced by a dual-beam laser, and the addition of the copper-foil interlayer might improve the metallurgical reaction of interfacial reaction region and promote the loadcarrying ability of weld joint. An ideal joint with fewer defects could be obtained when the welding speed is 0.9-1.25 m/min of dual-beam laser welding and 1.5-1.75 m/min of singlebeam laser welding.