Poly(vinyl pyrrolidone) (PVP)-based carbon/Fe3C composite nanofibers (C/Fe3C CNFs) have been successfully prepared by carbonization of as-electrospun PVP/ferric nitrate nanofibers. Unlike the pristine PVP nanofibers, the PVP/ferric nitrate nanofibers can retain fibers structure after carbonization, in which Fe3C nanoparticles are well-dispersed. More importantly, the as-prepared wax composites exhibit high electromagnetic wave absorption abilities, which can be attributed to the formation of the C/Fe3C CNFs “conductive network”, and leads to a more effective dielectric loss in terms of dissipating the induced current in the wax composites. Specifically, the CNFs/wax composites with a low filler ratio of 10wt% shows the minimum reflection loss of −62.6dB at 11.25GHz in a thin matching thickness of 3.6mm, and the effective bandwidth below −10dB can reach up to 6.5GHz. Thus, this work demonstrates a facile, cost-effective synthesized strategy to prepare carbon-based lightweight composite nanofibers with superior electromagnetic wave absorption properties.