The invention discloses a preparation method of nuclear-grade zirconium alloy return scrap cast ingots. The preparation method comprises the steps that 1, nuclear-grade zirconium alloy return scrap isidentified and classified; 2, pretreatment is conducted on the zirconium alloy return scrap same as nuclear-grade zirconium alloy return scrap cast ingots in mark or containing similar chemical component to the cast ingots; 3, the zirconium alloy return scrap subjected to pretreatment is selected and prepared into a consumable electrode and a zirconium block; 4, vacuum consumable smelting is conducted on the consumable electrode and a zirconium block to obtain the nuclear-grade zirconium alloy return scrap cast ingots. According to the mass content of O and N in the nuclear-grade zirconium alloy return scrap cast ingots, the nuclear-grade zirconium alloy return scrap containing different mass contents of O and N is selected, the mass contents of O and N in the nuclear-grade zirconium alloy return scrap cast ingots are accurately controlled, the nuclear-grade zirconium alloy cast ingots containing components conforming to GB/T13747 zirconium and zirconium alloy chemical analysis methodare obtained, effective recovery of zirconium alloy return scrap is achieved, and the recovery rate of the zirconium alloy return scrap is greatly improved.