The invention discloses a preparation method of oxidized polyethylene wax. The preparation method comprises the following steps: adding a given amount of raw material polyethylene into a reaction kettle, introducing nitrogen to purge the oxygen, stirring, heating to facilitate the cleavage reaction, then cooling, discharging the material, heating the prepared polyethylene wax to a temperature greater than a wax melting point, stirring, introducing oxidant gas at a set gas flow rate, continuously heating to a needed reaction temperature, reacting for a given time, after the reaction is ended, cooling, discharging, and obtaining the oxidized polyethylene wax. The preparation method has the beneficial effects that the high density polyethylene resin, low density polyethylene resin or waste polyethylene plastics are used as a raw material, the raw material can be selected according to a use and the cost, the waste can be effectively utilized, and the environmental protection is facilitated; the oxygen-containing gas is directly introduced into the wax melt, so that the preparation method has the advantages of low cost, simple process and the like; and meanwhile, by controlling variousreaction conditions, the cross-linking reaction in the oxidation process can be reduced, so that the viscosity and acidic value of a product can be ensured to reach the standard.