The invention provides a preparation method and application of a carbon nanohorn/graphene/polyaniline composite material, belonging to the field of composite material preparation. The preparation method of the carbon nanohorn/graphene/polyaniline composite material comprises the following steps: firstly preparing graphene oxide with a large specific surface area; uniformly mixing carbon nanohorns with a graphene oxide aqueous solution, and adding aniline monomers under an acidic condition; and preserving heat at a selected temperature after uniformly stirring, adding an acidic aqueous solution of an initiator, reacting for a certain time at the selected temperature, so as to obtain a carbon nanohorn/graphene oxide/polyaniline composite material, and reducing graphene oxide under the action of a reducing agent so as to obtain the carbon nanohorn/graphene/polyaniline composite material. The prepared carbon nanohorn/graphene/polyaniline composite material can be used as an electrode material of a supercapacitor. The preparation method is simple and feasible, and the composite material has excellent comprehensive performance. The preparation method provides a new way for application of the composite material in the aspect of the supercapacitor.