The invention relates to a nano conductive polymer/graphene composite fiber, and a preparation method and application thereof. The section of the fiber is special; a graphene sheet is at a loose stacking state; enriched fold morphology is formed on the surface of the fiber; the average strength of the fiber is greater than 50 MPa; the average breaking elongation is greater than 2 percent; the average conductivity is greater than 1 S/cm. The method comprises the following steps: preparing conductive polymer/graphene oxide composite spinning solution; then extruding the solution into a coagulating bath and performing elongation and curing, and performing drying and winding on the obtained wet fiber, so as to obtain conductive polymer/graphene oxide composite fiber; finally performing reduction through a chemical or physical method so as to obtain the nano conductive polymer/graphene composite fiber. The nano conductive polymer/graphene composite fiber has the advantages that an adjustable special section structure is formed on the section of the composite fiber, rich microstructures are formed on the surface of the composite fiber, the problem that graphene sheet layers are closely stacked is overcome, the graphene fiber with pure toughness is greatly enhanced, and excellent conductivity of the graphene fiber is still kept, so that the composite fiber has a wide application prospect.