The invention relates to the technical field of carbon materials, in particular to composite activated carbon aerogel as well as a preparation method and application thereof. According to the method,cellulose pulp and carbon nanotubes are used as raw materials, and the weight ratio of the cellulose pulp to the carbon nanotubes is (8-10): 5. According to the invention, cellulose is used as a carbon aerogel matrix, so that agricultural wastes can be recycled, the problems of environmental pollution, resource waste and the like are reduced, the electrochemical performance of the cellulose carbonaerogel is greatly improved by doping the carbon nanotubes, and the cellulose carbon aerogel can be widely applied to the field of supercapacitors.