The invention provides a preparation method for high-toughness nodular cast iron, which is a method for producing high-toughness nodular cast iron by utilizing a medium-frequency electric furnace and selecting materials such as cast iron which is low in sulfur, phosphor and manganese content, waste steel, and the like. The preparation method mainly comprises chemical component design, furnace burden selection, medium-frequency furnace smelting, a nodulizing agent selection and nodulizing treatment method, a nucleating agent selection and nucleating treatment method, and the like. The method disclosed by the invention does not need thermal treatment and desulfuration treatment, is less in processes, adopts a wet type sand production line to manufacture QT600-10 casting pieces, has casting efficiency higher than that of sand-lined iron type, and is low in cost. The produced nodular cast iron is high in strength, good in plasticity and toughness, can be used for components such as a transmission shaft, a rear axle shell, a differential mechanism shell, a bracket, and the like for a car and a tractor chassis.