The present invention relates to the field of building surface coating technologies, and in particular, to an alumina sol-silane composite material and a preparation method and application thereof. The alumina sol-silane composite material provided in the present invention is prepared by raw materials including the following components by weight parts: 5 to 45 parts of alumina sol, 30 to 90 parts of silane, 3 to 10 parts of silane coupling agent, and 1 to 5 parts of dispersant. A hydrophobic anticorrosive coating can be formed after coating the alumina sol-silane composite material provided in the present invention to a surface of a cement-based material, and has good waterproof performance and corrosion resistance.