A carburized alloy steel and a method for preparing same. The elements of the alloy are present in the following mass percentages: C: 0.15%-0.25%, Si: ≤0.30%, Mn: 0.30%-1.20%, P: ≤ 0.015%, S: ≤ 0.010%, Cr: 0.30%-1.50%, Ni: 2.80%-3.80%, Mo: 0.30%-1.00%, Al: 0.01%-0.08%, and at least one of V: 0.05%-0.15% and Nb: 0.025%-0.10%, the remainder being Fe and unavoidable impurities; and the mass percentage content of V, Nb and Al satisfies V+Nb+Al≤0.30%. The carburized alloy steel is obtained by means of smelting, blank casting, normalizing/tempering treatment, and quenching/tempering treatment. The quenching treatment involves increasing the temperature of a blank to 800°C-860°C, maintaining the temperature for 0.8h-1.5h, then placing into a rapid quench oil to cool to the temperature of the rapid quench oil.