The invention relates to cast iron, in particular to a preparation method of spheroidal graphite cast iron. The preparation method aims to improve the yield ratio of conventional spheroidal graphite cast iron and increase the elongation rate on the premise that the strength is not changed. The preparation method comprises the following steps of 1 material proportioning, taking waste steel, pig iron and return material with the ratio of 20%:60%:20%; 2, adding graphite core; 3, fine adjusting of components; 4, overheating treatment; 5, ending heat preservation; 6, spheroidizing treatment; 7, inoculation treatment; and 8, pouring. According to the preparation method, the technology of the material is broken through, the conventional performance of the material is effectively improved, the strength is increased, and the extension is not reduced and even increased; and the comprehensive performance, the processing performance, the stability and the operability of the material are improved,meanwhile, the production cost is reduced, and the purpose of light weight of the product can be achieved.