The invention provides a mildew-proof preservative paper and a preparation method and a preparation device thereof. The preparation device comprises a paper-based layer, a decorative coating and a mildew-proof preservative coating, wherein the mildew-proof preservative coating is arranged one surface of the paper-based layer, the decorative coating is arranged on the other surface of the paper-based layer, the mildew-proof preservative coating is made from a mildew-proof preservative coating raw material and is prepared from, by weight, 20%-60% of resin, 30%-70% of solvent, 0.5%-10% of mildew preventive and 0.3%-5% of additive, the resin is at least one of polyurethane resin, acrylic ester copolymer, polyvinyl alcohol, polyvinylidene chloride, modified polyethylene vinylidene chloride, vinyl-vinyl acetate copolymer, polyvinyl acetate copolymer and vinyl acetate-butyl copolymer, and the solvent is at least one of water and ethanol. The surface of the obtained mildew-proof preservative coating is dense and provided with small pores, the mildew-proof preservative coating has the good effect keeping moisture constant, the mildew preventive is dispersed inside resin, mildewing can be also prevented, and further a good preservation effect is reached.