The invention relates to a preparation method of an Al-Zn-Mg alloy. The preparation method of the Al-Zn-Mg alloy comprises the following components of, in percentage by weight, 0.12%-0.18% of Si, 0.12%-0.18% of Fe, 0.15%-0.25% of Cu, 0.03%-0.1% of Mn, 0.7%-1.5% of Mg, 5.5%-6.0% of Zn, 0.15%-0.25% of Zr, 0.08%-0.2% of Ti, and the balance Al and inevitable impurities; and the preparation method comprises the specific preparation steps of smelting, casting, homogenizing annealing, extrusion, cooling, pretreatment and subsequent treatment. The Al-Zn-Mg alloy material prepared through the method has a smaller recrystallization structure, higher strength, better corrosion resistance, better room-temperature mechanical performance, better bending forming performance, better welding performance and the like, and industrial batch production of Al-Zn-Mg alloy bumper profiles can be achieved.