Since the matching between the complex permittivity and permeability plays a dominant role in the performance of microwave absorbing, magnetic-dielectric materials have been increasingly used for microwave absorption. In this paper, Fe3O4 nanoparticles anchored on carbon nanotubes (Fe3O4@CNTs) were fabricated via a self-assembled technique. The efficient microwave-absorbing fabric was synthesized by building polyaniline nanofibers (PANI NFs) and Fe3O4@CNTs magnetic–dielectric network on the surface of polyimide (PI) fabric. The results of SEM, FTIR, and XRD demonstrated the presence of Fe3O4@CNTs on the fabric surface. The decomposition temperature (Td) of the fabric was beyond 580.0 °C and the fabric exhibited strong hydrophobicity (water contact angle 125.0°). The Fe3O4@CNTs/PANI/PI fabric possessed a minimum reflection loss (RL) value of −62.61dB (>99.9% absorption) with a matching thickness of 1.58 mm. The excellent microwave absorption capacity is attributed to the well impendence match, dielectric and magnetic loss, and the scattering loss of the special cell structure.