The invention belongs to the technical field of the chemical modification of nano bacterial cellulose and the compositing of modified nano bacterial cellulose and a conducting macromolecule, and particularly discloses an ionized BC/PANI (Bacterial Cellulose/Polyaniline) flexible double-conducting composite material as well as a preparation method and application thereof. The method comprises the following steps of first, carrying out pretreatment and purification on originally ecological nano bacterial cellulose; subsequently, carrying out the chemical modification on the nano bacterial cellulose subjected to the pretreatment and the purification to introduce a functional group; in situ synthesizing polyaniline on the nano bacterial cellulose subjected to the chemical modification, so as to obtain an ionized nano BC/PAN flexible double-conducting composite material; the functional group introduced by carrying out the chemical modification on the nano bacterial cellulose subjected to the pretreatment and the purification comprises any one of carboxymethyl, a carboxylate-radical ion and a sulfonate-radical ion. The composite material prepared and obtained by the preparation method not only has the excellent electronic conductivity of the polyaniline, but also has better ionic conductivity through a chemical group introduced through modification.