The invention relates to a preparation method of a nanocellulose/carbon nanotube/polydimethylsiloxane conductive composite film, and a conductive composite film prepared by the method. The preparationmethod comprises the following steps: extracting cellulose from wood flour; preparing nanocellulose by a mechanical grinding method; preparing a nanocellulose/carbon nanotube composite film; and preparing the nanocellulose/carbon nanotube/polydimethylsiloxane conductive composite film by an impregnation method. The nanocellulose/carbon nanotube/polydimethylsiloxane conductive composite film prepared by the method has good flexibility and electrical conductivity.