The invention discloses a method for preparing 4, 4'-diphenyl ether dicarboxylic acid, which comprises the following steps: 1, adding 4, 4'-dimethyl ether, catalysts, organic acids as solvents and bromide as oxide additives into a reaction device; 2, adopting a bubbling method for introducing oxygen under the liquid level of the solvent in the reaction device, and heating the mixture to 110 to 160 DEG C for oxidation reaction for 1 to 10 h, or adopting an intermittent method for pressing the oxygen into the reaction device in two to five times, pressurizing to 1.0 to 4.0 MPa, and simultaneously raising the temperature to 110 to 160 DEG C for oxidation reaction for 1 to 10 h; and 3, carrying out cooling, suction filtration, washing and drying on materials after the reaction. The method of the invention has few steps, short time and easy post treatment, and is applicable to industrial large-scale production, wherein the high-pressure oxidation method also has the advantages of little catalyst consumption, high yield and the like.