The invention discloses an oil washing agent for carbon dioxide displacement as well as a preparation method and application thereof, and belongs to the field of carbon dioxide displacement oil extraction. The preparation method of the oil washing agent comprises the following steps: reacting a first monomer with formaldehyde in formic acid to obtain a first reactant; reacting the first reactant with borane, adding an oxidizing agent, and reacting under an alkaline condition to generate a second reactant; and reacting the aromatic hydrocarbon and a second monomer to obtain a third reactant, and reacting the second reactant and the third reactant under the heating condition to obtain the oil washing agent, wherein the first monomer is selected from at least one of 3-phenyl-4-pentene-1-amine, 4-pentene-1-amine, 4-methyl-pentene-1-amine and 2-amino-4-pentenoic acid; the second monomer is selected from at least one of succinic anhydride, 2,3-dimethyl succinic anhydride, glutaric anhydride and adipic anhydride; and the aromatic hydrocarbon is selected from at least one of benzene, methylbenzene and ethylbenzene.