The invention relates to the technical field of aluminum alloy ladder preparation, and particularly relates to high-strength antibacterial aluminum alloy for an aluminum alloy ladder and a preparation method thereof. The aluminum alloy comprises a high-strength aluminum alloy matrix and a micro-arc oxidation film, wherein the micro-arc oxidation film is arranged on the surface of the aluminum alloy matrix, the weight of a hole sealing agent on the micro-arc oxidation film is 0.15 g / cm<2> to 0.90 g / cm<2>, and the hole sealing agent covers at least 92% of micropores in the micro-arc oxidation film. The preparation method comprises the steps of smelting metal, modifying, refining and degassing, pouring and forming and performing quenching treatment, aging treatment, micro-arc oxidation and hole sealing treatment, wherein in the step of modifying, nanometer modificators are uniformly dispersed into liquid alloy obtained by smelting; in the step of refining and degassing, 0.23% to 0.38% of hexachloroethane is added to the modified liquid alloy so as to refine and degas; and the aging treatment is divided into four-stage aging treatment. The aluminum alloy prepared by adopting the preparation method has the characteristics of high hardness, high strength, wear resistance, corrosion resistance, good anti-cracking performance, good antibacterial effect, difficulty in aging and deformation and long service life.