The invention discloses a preparation method of a non-vacuum downward-casting copper-zirconium alloy slab ingot. The preparation method comprises the following steps: S1, carrying out burdening: weighing required raw materials according to percentage; S2, carrying out smelting: installing an electrolytic copper plate into a furnace, adding a covering agent, a copper-magnesium alloy, titanium and rare earth Re in sequence for smelting after the copper plate is molten, preparing molten copper for discharging after smelting is finished, and keeping the temperature of the molten copper at 1,200-1,300 DEG C; S3, adding the alloy: sealing a tundish with a cover plate, starting a heating device, discharging the molten copper, pouring the molten copper into the tundish, calculating a copper-zirconium alloy according to 5-10% of burning loss, and adding the copper-zirconium alloy into the tundish at intervals; and S4, performing continuous casting: performing downward-casting through a slab ingot crystallizer pipe. By adopting the preparation method, the problem that zirconium cannot be continuously added during the preparation of the copper-zirconium alloy is solved, and the problem that the uniformity of zirconium in a substrate is difficult to ensure is solved in a preparation process, so that a final material has uniform performance, the preparation requirement is met, and the material has high reproducibility.