The invention relates to a waterproof and air-permeable elastic film and a preparation method thereof. The elastic film contains the following components: matrix resin, elastomer resin, an antibacterial master batch, an inorganic powder material and an aid. The preparation method comprises the following steps: (S1) crushing the inorganic powder material, adding the matrix resin, the elastomer resin, the antibacterial master batch, and the crushed inorganic powder material into a high-speed kneading machine, stirring, adding the mixture into a double screw granulator, and carrying out granulation, extrusion, grain dicing and cooling, so as to obtain a resin master batch for later use; and (S2) uniformly mixing the resin master batch obtained in the step (S1) with the aid, carrying out internal mixing and plastification so as to obtain a sizing material, filtering, carrying out calendering by virtue of a calendering machine, carrying out cooling shaping by virtue of a cooling wheel set,and carrying out clipping and reeling, so as to obtain the elastic film. The prepared elastic film has the waterproof and air-permeable properties and has the advantages of good waterproof and air-permeable properties and antibacterial effect and simple preparation process.