The large-scale preparation of a homogeneous multi-dimensional assembly for microwave absorbers is still believed to be a huge challenge. Herein, a novel class of Fe₂O₃/CNTCM@CN hybrids featuring a three-dimensional (3D) hollow structure (d < 6.88 μm) was successfully fabricated by a facile spray-drying process, followed by an annealing treatment. Magnetic-dielectric composite microspheres were obtained by forcibly assembling 0D γ-Fe₂O₃ nanoparticles, 1D carbon nanotubes (CNTs), and 2D N-doped carbon layers. Due to the unique design of its interface structure and abundant electron conduction paths, Fe₂O₃/CNTCM@CN-2 exhibited excellent microwave absorption (MA) performance. Impressively, the MA value was enhanced to −51.5 dB for Fe₂O₃/CNTCM@CN-2 with a thickness of only 2 mm, and the efficient absorption bandwidth (<10 dB) was broadened to 5.4 GHz with only 10% loading mass; these values have surpassed those of most of the state-of-art MA materials. In this heterogeneous system, remarkable multi-interface regions were built by compressive contact among CNTs, nanoparticles, and N-doped carbon layers, which played a key role in promoting the interfacial polarization. Electron charge density redistribution observed by electron holography further supports the presence of dielectric relaxation locally around these contact interfaces. The special 3D CNT networks and bridged N-doped carbon layers enriched the electron transport routes and optimized the conductivity. In addition, spray-dried Fe₂O₃/CNTCM@CN absorbers at micron-size exhibited a better electromagnetic and size matching. Therefore, this study provides deep insights into a novel strategy for the construction of multi-dimensional hollow assemblies as MA candidates.