The invention provides a preparation method and application of a cobaltosic oxide/graphene aerogel composite material. The cobaltosic oxide/graphene aerogel composite material can be used in the field of colorimetric method based detection, especially used for colorimetric method based acetyl choline detection. A water solution prepared by oxidized graphene and soluble cobalt salt is transferred into a cylindrical container, then the cylindrical container is moved into a polytetrafluoroethylene hydrothermal kettle to perform constant-temperature thermal reaction, a drying technology is adopted to prepare the cobaltosic oxide/graphene aerogel composite material, and the preparation method is simple. The prepared cobaltosic oxide/graphene aerogel composite material has excellent conductivity, good electronic transmission performance and large localization range, and catalytic effect is remarkably improved. The prepared cobaltosic oxide/graphene aerogel composite material is creatively applied to colorimetric method based acetyl choline detection, operation is simple and convenient, the used instruments are low in price, and the research field of graphene aerogel based materials is widened.