Abstract To reduce electromagnetic interference (EMI) and irradiation, one efficient path is to develop electromagnetic absorption (EMA) material with the aim of high-efficient convert electromagnetic wave into thermal energy. Presently strategy to design high-performance electromagnetic absorber is followed by the way of component optimization and microstructure design. This research reported an advanced HWCNTs/Fe@Fe3O4 ternary absorber, which was fabricated by decorating H2O2 treated carbon nanotubes (HCNTs) with magnetic core-shell shaped Fe@Fe3O4 nanoparticles. This HCNTs/Fe@Fe3O4 composite exhibits various electromagnetic loss forms, including conductive, dipole, interface loss etc. which attribute to EMA ability. The largest qualified frequency width (fE) can up to 5.4 GHz with a thickness of 1.5 mm. To discuss the EMA loss mechanism, control experiments have been conducted by preparation of Fe@Fe3O4, HCNTs@Fe@Fe2O3 composites. In this way, the attenuation mechanism can be better understood.