The invention relates to the technical field of filter paper preparation, and discloses antibacterial oil-air filter paper and a preparation method thereof. The antibacterial oil-air filter paper andthe preparation method thereof solve the problem that in the prior art, the degradation of the filter paper by bacteria reduces the mechanical properties and the filtration performance of the filter paper. The preparation method of the oil-air filter paper comprises the steps that ramie fiber, cotton fiber and bamboo fiber are mixed for beating to form slurry, modified activated clay is added to the slurry, the mixture is stirred and mixed uniformly, and then the slurry is fed to a top wire former for papermaking to obtain base paper; then the base paper is immersed in an aqueous solution of carboxymethyl cellulose and an aqueous solution of a polyhydroxy flavonoid compound for crosslinking to obtain antibacterial base paper; and finally, the antibacterial base paper is immersed in a water-soluble phenolic resin solution to obtain the antibacterial oil-air filter paper. The oil-air filter paper has good antibacterial effect, thereby being longer in service life.