The invention discloses a super-hydrophilic and underwater super-oleophobic oil-water separation mesh membrane, and its preparation method. The method comprises the following steps: 1, cleaning a copper mesh, and airing; 2, dissolving an alkaline medium and an oxidant in water, and uniformly stirring to obtain a mixed solution; and 3, dipping the aired copper mesh in the mixed solution, and carrying out an oxidation reaction to obtain the oil-water separation mesh membrane. The oil-water separation mesh membrane has the advantages of easily available raw material, low cost, simple equipment and making technology, realization of large-scale preparation, large water flux, fast water-water separation speed, good oil-water separation effect, suitableness for the treatment of sewage containing a large amount of water, very good separation effect on n-hexane, petroleum ether, dichloroethane, benzene, gasoline, diesel oil, kerosene, machine oil, crude oil, animal and plant oil, and the like, easy cleaning, repeatable use, and good stability.