The invention relates to isothermal quenching nodular cast iron as well as a preparation method and application thereof. The isothermal quenching nodular cast iron is prepared from the following components of, in percentage by weight, 3.60%-3.75% of C, 2.30%-2.50% of Si, 0.20%-0.40% of Mn, less than or equal to 0.06% of P, less than or equal to 0.03% of S, 0.70%-0.80% of Cu, 0.10%-0.20% of Mo, 0.03%-0.06% of Mg, and the balance Fe; and the preparation method of the isothermal quenching nodular cast iron comprises the following steps that (1) nodulizing inoculation is conducted on molten iron by adopting a pouring nodulizing method, pouring is conducted after the inoculation is completed, and after pouring is completed and cooling is conducted, the nodular cast iron is obtained; and (2) thenodular cast iron obtained in the step (1) is sequentially subjected to preheating, austenitizing and salt bath quenching, and the isothermal quenching nodular cast iron is obtained after the salt bath quenching is completed. According to the isothermal quenching nodular cast iron as well as the preparation method and the application thereof, the problems that the performance of an axle housing does not reach the standard and the like when the isothermal quenching nodular cast iron material is used for integrated manufacturing are solved, and efficient utilization of the isothermal quenchingnodular cast iron in the integrated axle housing is achieved.