The invention relates to a microporous polyethylene breathable film and a preparation method thereof. The film is obtained by a coextrusion blow molding method, and comprises a printing layer, a middle layer and a heat-sealing layer, wherein each of the printing layer, the middle layer and the heat-sealing layer is prepared from calcium carbonate, metallocene linear low density polyethylene and a fluorine-containing processing agent with a mass ratio of (65 to 75):(25 to 35):(0.5 to 1.5), and the particle size of the calcium carbonate is 1 to 2 mu m. The microporous polyethylene breathable film has obvious advantages in indexes such as pulling strength, hydrostatic pressure and water vapor permeability, thus providing excellent technical guarantee for positioning, cutting and multi-colour printing chromatography of corresponding products; the gram weight of per unit area of the microporous polyethylene breathable film is light, thus plastic resin can be used less, energy consumption is greatly reduced, and carbon emission is reduced, thus providing guarantee for realizing lightness and emission reduction of one-off living sanitary articles.