The invention discloses a preparation method of a silver monoatom/manganese dioxide composite catalyst of an aluminum-air battery, and relates to the technology in the field of metal-air batteries. The invention aims to solve the problems of low silver conversion rate and high preparation cost in the existing preparation method of the aluminum-air battery catalyst. The method comprises the steps:1, preparing manganese dioxide; 2, preparing manganese dioxide rich in oxygen vacancy; 3, preparing manganese dioxide impregnated with silver nitrate; 4, calcining the manganese dioxide impregnated with silver nitrate at the high temperature of 500-1,000 DEG C under an inert atmosphere to obtain the silver monoatom/manganese dioxide composite catalyst. According to the invention, the generation ofsilver monoatoms can reduce the use cost of silver in the preparation of the catalyst; the manganese dioxide with oxygen-enriched vacancies is utilized, and the catalytic efficiency of silver atoms is effectively improved; the use amount of silver in the production process of the aluminum-air battery is integrally reduced, and the conversion rate of silver is improved by 15%-20%; the preparationcost is reduced, and the production cost is effectively reduced by 10%-15% in commercial mass production.