Synchronous enhancement and broadening of dielectric loss and magnetic loss is a key factor for achieving excellent microwave absorption behavior. However, one term’s reinforcement always comes at the expense of the other one. In this work, a new kind of core-shell structured nanoparticle has been designed and prepared by arc-discharge method, in which GdFeO3 is shell and Fe (Gd) solid solution works as core, respectively. Except for the typical interfacial polarization and natural resonance, the new dipole induced by asymmetric electric charge arising from substituted Gd in Fe lattice results in enhanced and broadened dielectric loss, and the strong local magnetic anisotropy induced by intensive magnetic Fe-Gd coupling between 3d-4 f electrons leads to enhanced and broadened magnetic loss. Synchronously widened and enhanced dielectric and magnetic loss ensure that GdFeO3-encapsulated Fe(Gd) nanoparticles have effective absorption bandwidth of 4.16 GHz (10.48–14.64 GHz) at 2.3 mm, compared with that (2.32 GHz at 4.9 mm) of Fe nanoparticles. This study develops an approach for synchronously enhancing dielectric loss and magnetic loss, which has potential for achieving excellent EM absorption behaviors.