The invention provides a method for degrading polyethylene glycol terephthalate (PET). The method comprises the steps of preparing HAP-gamma-Fe2O3, preparing a 1-methyl-3-(3-propyltriethoxysilane) imidazole chloride, preparing a magnetic ion liquid, pretreating a raw material, carrying out catalytic reaction by adopting the catalyst and purifying the product, wherein in the step of carrying out catalytic reaction, PET, the magnetic ion liquid and water are put into a reaction kettle, the mass ratio of PET to the magnetic ion liquid is 1:(0.05-0.15), and the temperature is set to be 200-320 DEG C and the time is set to be 15-30 hours; and after the reaction kettle is cooled to the room temperature after reaction is completed, stirring, standing and layering are carried out, suction filtration is carried out, NaOH is added to the filtrate, suction filtration is carried out again, HCl is added and suction filtration is carried out, thus obtaining a product terephthalic acid. By degrading PET by adopting the method provided by the invention, the degradation rate can be more than 90%.