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[Display omitted] • Controlling the load of Co-CoFe 2 O 4 can receive exceptional impedance matching. • The minimum reflection loss is −65.31 dB at 2.1 mm. • The maximum effective absorption bandwidth is 8.48 GHz at 2.4 mm. Carbon nanomaterials have attracted a great deal of attention in various fields especially in electromagnetic wave absorption due to unique physical and chemical properties. Herein, a novel Co-CoFe 2 O 4 @mesoporous hollow carbon spheres (PCHMs) nanocomposites were prepared by two-facile steps, which included synthesizing three-dimensional mesoporous hollow carbon nanospheres (3D PCHMs) by hard template method, pyrolysis and etching process and in-situ growth of ultra-small Co-CoFe 2 O 4 nanoparticles on PCHMs. The microscopic morphology and electromagnetic wave absorption mechanisms were discussed in depth. The synthesized Co-CoFe 2 O 4 @PCHMs maintained a stable hollow and mesoporous structure and the Co-CoFe 2 O 4 nanoparticles are uniformly distributed on the PCHMs. The complex permittivity and complex permeability could be effortlessly controlled by the content of Co-CoFe 2 O 4 nanoparticles. Benefitting from the remarkable impedance matching under the influence of moderate complex permittivity and complex permeability, the minimum reflection loss (RL min) of S2 exhibited −65.31 dB at 2.1 mm. The maximum effective absorption bandwidth (EAB) reached up to 8.48 GHz. The Co-CoFe 2 O 4 @PCHMs nanocomposites will have great potential application in electromagnetic wave absorption. [ABSTRACT FROM AUTHOR]