The invention provides a preparation method of an amphoteric-ion molecular deposition film oil displacement agent for tertiary oil recovery. The preparation method comprises steps as follows: 60-70 parts by mass of a trimethylamine aqueous solution, 20-30 parts by mass of a chloroacetic acid aqueous solution and 10-20 parts by mass of epichlorohydrin are mixed and then are subjected to a thermostatic reaction at the temperature of 70-80 DEG C, pH is controlled to be 8-9 with alkali in a reaction process, reduced-pressure distillation is performed after the reaction, acid is added, white crystals are separated out, the white crystals and inorganic base are dispersed in isopropyl alcohol, chloroethanol is added dropwise, the temperature is increased to 50-55 DEG C, the reaction is performed for 4-5 h, a mixture is subjected to the reduced-pressure distillation, and a transparent thick pale yellow liquid is obtained and is the amphoteric-ion molecular deposition film oil displacement agent for the tertiary oil recovery. The oil displacement agent has good oil displacement performance, and the oil displacement efficiency is increased by 18% or higher.