The invention belongs to the technical field of zirconium alloy preparation and particularly relates to a preparation method of a nuclear-grade zirconium alloy cast ingot. The preparation method comprises the following steps that (1) the alloy component and the total mass of the finished cast ingot are determined; (2) an intermediate alloy and an alloy cladding are prepared; (3) material mixing isconducted; (4) electrode pressing is conducted; (5) N electrodes are welded into one electrode; (6) vacuum self-consuming arc melting is conducted; and (7) surface machining and dead head cutting areconducted. According to a technology suitable for industrial scale production and used for preparation of the Zr-Sn-Nb-Fe/Cr zirconium alloy cast ingot, the technological economical efficiency can beobviously improved, meanwhile component evenness control over the cast ingot is superior to that of a traditional technology, and the preparation method can be used for industrial scale production ofthe nuclear-grade zirconium alloy cast ingot accordingly.