The invention discloses a feed additive and a preparation method and an application thereof. A novel feed additive capable of absorbing zearalenone is prepared by utilizing hexadecyl trimethyl ammonium bromide tetraethoxysilane as a raw material. The preparation method is as follows: reacting hexadecyl trimethyl ammonium bromide with tetraethoxysilane to obtain white solid. In order to prevent the hexadecyl trimethyl ammonium bromide from losing in the solution, the white solid can be further performed with surface treatment in the following method: soaking the white solid in a sodium alginate solution and/or a chitosan with pH of 4-6 to form a layer of netty structure on the surface.