The invention relates to a method for modifying mesoporous silicon. The method provides a photoinitiator and an organic compound, the photoinitiator has a benzoyl group and a terminal hydroxyl group,the terminal hydroxyl group and the acyl group of the benzoyl group are located at a para-position, an ortho-position or a meta-position of a benzene ring of the benzoyl group, the organic compound contains a sulfonyl or methoxycarbonyl group, in a first solvent with a first basic environment, the sulfonyl or methoxycarbonyl group replaces a hydrogen atom of the terminal hydroxyl group to form a sulfonate or methoxylate group so that a sulfonate or methoxylate-modified photoinitiator is obtained, the method provides mesoporous silicon, the surface of the mesoporous silicon is modified with anamino group, in a first inert gas protective atmosphere, in a second solvent with a second basic environment, an amino group replaces a sulfonate or methoxylate group so that the photoinitiator modifies the surface of the mesoporous silicon, the method provides a monomer, and under ultraviolet light irradiation and second inert gas protection, the photoinitiator forms a benzoyl free radical and causes monomer polymerization so that the surface of the mesoporous silicon forms a polymer molecular brush.