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The development of wide-band microwave absorbing materials based on carbonaceous fillers remains a great challenge. In this study, carbon nanotubes (CNT) assembled coronal hollow clusters with efficient microwave absorbing performance have been obtained through successive hydrothermal and calcination process. Microstructural analysis reveals the distinct features of multiple assembly structures in the fabricated materials. The electromagnetic responses of Ni/CNT assembled clusters were examined across a frequency range of 2–18 GHz. Results demonstrate that the microwave frequency dispersion of electromagnetic parameters and reflection loss of Ni/CNT clusters are strongly influenced by weight loading. Multi-absorbing peaks with reflection loss better than − 40 dB could be achieved, while the equivalent absorbing band for RL < −10 dB covers 3.2–18 GHz, which account for 92.5% of the whole evaluated frequency range, and 62.5% for condition of RL < −20 dB. Furthermore, intrinsic attenuation beyond thickness derived semi-wavelength resonant absorption makes a major contribution to this superior performance. The underlying mechanism of dielectric response was investigated through Cole-Cole analysis and finite element simulation. 'Micro-dipoles' relaxation and hopping relaxation originated from defects within CNT and barrier between CNT, while the high magnetic dissipation capability of Ni nanoparticles make a major contribution to overall absorbing performance. All these are beneficial to regulation and optimization of microwave absorption performance of novel Ni/ CNT functionalized multistage architecture. [Display omitted] • Ni/CNT clusters were prepared through a sample solvothermal method; • Carbon nanotubes were assembled in situ into coronal hollow spherical multilayer carbon nanotube clusters; • The absorption efficiency of CNT is improved by anisotropic strong dielectric loss and multi-layer structure. • The microwave absorption of the new Ni/ CNT functionalized multistage structure greatly improves the performance. [ABSTRACT FROM AUTHOR]