This study presents the construction of hierarchical Fe3O4-Fe@CNFs/Al-Fe3O4-Fe nanocomposites through in situ growth, vacuum-assisted filtration, and self-reduction methods. The nanocomposites exhibit excellent electromagnetic wave absorption properties, achieving a minimum reflection loss (RLmin) of −59.3 dB at 6.6 GHz with a thickness of 4.3 mm, and an effective absorption bandwidth (EAB) of 5.6 GHz at 2.2 mm. The hierarchical structure, featuring a 3D carbon framework and magnetic nanoparticles, enhances impedance matching and dielectric polarization. The 0D Fe3O4-Fe nanoparticles, 1D carbon nanofibers, and 2D Al-Fe3O4-Fe nanosheets contribute to the efficient absorption performance. The material's superior properties are attributed to its multi-dimensional gradient structure, multiple loss mechanisms, and synergistic effects of its components. These findings provide valuable insights into the design of high-efficiency electromagnetic wave absorption materials.This study presents the construction of hierarchical Fe3O4-Fe@CNFs/Al-Fe3O4-Fe nanocomposites through in situ growth, vacuum-assisted filtration, and self-reduction methods. The nanocomposites exhibit excellent electromagnetic wave absorption properties, achieving a minimum reflection loss (RLmin) of −59.3 dB at 6.6 GHz with a thickness of 4.3 mm, and an effective absorption bandwidth (EAB) of 5.6 GHz at 2.2 mm. The hierarchical structure, featuring a 3D carbon framework and magnetic nanoparticles, enhances impedance matching and dielectric polarization. The 0D Fe3O4-Fe nanoparticles, 1D carbon nanofibers, and 2D Al-Fe3O4-Fe nanosheets contribute to the efficient absorption performance. The material's superior properties are attributed to its multi-dimensional gradient structure, multiple loss mechanisms, and synergistic effects of its components. These findings provide valuable insights into the design of high-efficiency electromagnetic wave absorption materials.