The invention belongs to the technical field of separating and purifying film materials, and provides a superhydrophobic modification method of a mesoporous polycarbonate/silica composite film. The method adopts a PC mesoporous tubular film as a hard template, an amino-modified SiO2 film is formed on the inner wall of a PC tubular film by an evaporation-induced self-assembling technology, cellulose acetate is adsorbed by the inner SiO2 layer and the outer PC layer of the composite mesoporous film, a trifluoromethanesulfonyl chloride gas is introduced, a reaction is carried out, and the surfaceof the PC film and the surface of the SiO2 film are grafted with -CF3 groups to realize the superhydrophobic modification of the composite mesoporous film. Compared with conventional methods, the modification method of the invention can obviously improve the hydrophobic properties of the inner SiO2 film and the outer PC film of the composite mesoporous film, and the modified composite mesoporousfilm can be used for treating oily sewage and treating marine petroleum pollution.