In order to study the influence of different laser power on swing welding steel/aluminum, the lap experiments of DP780 dual-phase steel and 5083 aluminum alloy were carried out by combining a high-power disc laser with a swing joint of PFO3D. The experimental results show that the plate welding can be effectively realized within the power range of 1400W~1600W. When the laser power is 1400W, the microstructure of the welded joint is low carbon martensite, and the lowest and highest microhardness are located in the heat affected zone and the weld center, respectively. With the increase of laser power, the amount of ferrite in the weld increases, while the amount of martensite decreases. The maximum and minimum values of microhardness of the joint are changed to heat affected zone and weld center, respectively. When the laser power is 1400W, the tensile strength of the weld is the highest, which is 2681MPa. The research results are of great significance in the field of shipbuilding.