The invention discloses a surface oxidation treatment method of an aluminum alloy die-casting mould. The surface oxidation treatment method of the aluminum alloy die-casting mould includes the following steps that mould steel is subjected to vacuum hardening and three times of tempering treatment at first, and the hardness of the mould steel is made to range from 42 HRC and 54 HRC; then the surface of the mould steel is cleaned; and the mould steel is fed into an ion nitriding furnace for oxidation treatment. According to the technical parameters, gas for the heating-up process is Ar, and the Ar flow in the heating-up process is 200-500 ml/min; the oxidizing temperature is 520-540 DEG C and is maintained for 2-4 hours; air serves as the oxidizing gas, and the air flow is 300-600 ml/min; voltage is 650-850 V; and the furnace pressure is 300-500 Pa. According to the surface oxidation treatment method of the aluminum alloy die-casting mould, Ar is applied to the steel ion oxidation heating-up process of a hot-working mould, a uniform and compact oxidation film is formed on the surface of the mould steel by controlling the air flow and furnace pressure in the steel oxidation process of the aluminum alloy die-casting mould, and thus the anti-melting-loss ability, the antisticking property and other surface qualities of an aluminum extruded mould are improved.