The invention relates to a preparation process of a Al-Zn-Mg alloy profile for a high-speed train body. The preparation process comprises the following steps that (1), extruding is carried out; (2), roll bottom continuous solution hardening is carried out; (3), stretching is carried out; (4), plate type three-stage aging oven for aviation aging treatment is carried out; (5), finished product saw cutting is carried out; and (6), packaging and storing are carried out. According to the preparation process of the Al-Zn-Mg alloy profile for the high-speed train body, roll bottom continuous solution hardening and plate type three-stage aging oven for aviation aging treatment are adopted for production, and thermal treatment precision can be greatly improved. Meanwhile, a gradient heating method is adopted during extrusion, the Al-Zn-Mg profile head and tail temperature difference is precisely controlled, the Al-Zn-Mg alloy profile head, middle and tail performance difference is reduced, and therefore the performance stability of the Al-Zn-Mg alloy profile is guaranteed.