Disclosed are an Al-Mg-Zn-Mn aluminum alloy welding wire and a preparation method thereof. The welding wire and the method belong to the technical field of aluminum alloys. The welding wire comprises,by mass, 0.5-3.0% of Zn, 4.5-5.5% of Mg, 0.4-1.0% of Mn, 0-0.15% of Ti, 0-0.15% of Cr, 0-0.25% of Fe, 0-0.25% of Si, 0-0.15% of the total amount of other impurity elements, 0-0.05% of single impurityelement and the balance Al. The preparation method comprises the steps of smelting, casting, preprocessing after heating to 200-400 DEG C and performing heat preserving for 2-6 hours, extruding afterperforming heat preserving under the temperature of 440-470 DEG C for 2-4 hours, rolling after heating to 480-550 DEG C and performing heat preserving for 2-4 hours, in-process annealing and bright-cold drawing. According to the method, high-temperature and long-duration uniform processing is not needed, energy is saved, processing procedures of welding wire are shortened, wire braking during drawing is reduced, yield of drawing is improved, production cost is reduced, and metal microstructure can be refined, so that weld metal has natural aging strengthening capability to improve the performance of weld joints.