The invention discloses a method for reducing internal superheat of casting metal. Superheat is directly lowered in the center of a large ingot by the aid of heat of molten metal, absorbed by a molten salt coolant melted in the center of the ingot, and segregation and shrinkage cavity defect are removed; the molten salt coolant is placed in the center of the ingot after casting, the heat around the molten metal is absorbed when the molten salt coolant is melted, the temperature of the center of the ingot is lowered, and formation of center segregation is suppressed; meanwhile, molten salt floating after being melt plays a role in slag insulation protection, crystalline latent heat is released from crystallization in the subsequent cooling process, function of exothermic riser is achieved, rehydration of the molten metal is benefited, and shrinkage cavity in the center of the ingot is reduced; the method is convenient in process and convenient for large-scale industrial production and application.