Graphene is a promising electromagnetic wave absorption (EMWA) material because of its structural designability, controllable electromagnetic properties, and excellent stability. However, the impedance mismatch caused by high conductivity and dielectric properties has seriously hindered the application of graphene in the EMWA field. In this work, based on the dielectric dispersion behavior of ideal broadband absorption as a guide, a Fe microsheet/reduced graphene oxide (Fe/RGO) composite was prepared by simple hydrothermal and thermal reduction methods. The permittivity of RGO is optimized by adjusting the content of anisotropic Fe microsheets, and a balance between attenuation ability and impedance matching is achieved. Theoretical calculations and off-axis electron holography results reveal that the abundant polar sites and heterogeneous interfaces of Fe and RGO enhance the dipole and interface polarizations. The three-dimensional (3D) conductive network structure contributes to multiple reflections of incident electromagnetic waves and conduction loss. The natural and exchange resonances and eddy current loss caused by anisotropic Fe microsheets further increase magnetic loss. Based on the dielectric-magnetic loss mechanism and good impedance matching, Fe/RGO achieves a minimum reflection loss (RL_min) of −67.95 dB at 8.48 GHz and a maximum effective absorption bandwidth (EAB_max) of 6.91 GHz (11.09–18 GHz) with a low filling content of 10 wt%. In addition, Fe/RGO has excellent radar stealth performance, with a radar cross section (RCS) of −31.21 dBm² at 0°. Therefore, the proposed strategy and theoretical analysis provide a reference for the microstructure design, composition, and mechanism analysis of EMWA materials.