The invention relates to the field of catalysts, preparation methods and applications thereof, in particular to a MnY catalyst for catalytically removing indoor formaldehyde and a preparation method thereof. The catalyst is composed of a catalyst carrier NaY molecular sieve and an active component Mn. Manganeseacetylacetonate (II) is a manganese source of the active component Mn. The preparation method comprises the following steps: soaking the NaY molecular sieve in an acetone solution of manganeseacetylacetonate (II), and stirring the mixture till an acetone solvent is fully volatilized to obtain a catalyst precursor; and carrying out temperature programming activation in an activated atmosphere, and then cooling the mixture to room temperature and taking the same out to obtain the MnY catalyst. The MnY catalyst prepared by the method removes formaldehyde in indoor air. As Mn oxide active centers which have good catalytic effects in oxidizing and removing formaldehyde are dispersed to the surface of the Y molecular sieve, formaldehyde adsorbed to the surface of the Y molecular sieve is degraded to CO2 and H2O without being affected by adsorption capacity. The method is concise, quick and environment-friendly, and shows a relatively good catalytic performance in catalytic removal of indoor formaldehyde.