Abstract: Advanced electromagnetic absorbing materials (EAMs) with strong absorption and a wide effective absorption bandwidth (EAB), using innovative microstructural design and suitable multicomponents remain a persistent challenge. Here, we report the production of a material by the hydrothermal reduction of a mixture of graphene oxide (GO), Ni(NO₃)₂·6H₂O, and Co(NO₃)₂·6H₂O, resulting in reduced GO (RGO) with a self-assembled 3D mesh structure filled with NiCo₂(CO₃)₃ . The unique microstructure of this assembly not only solves the problem of NiCo₂(CO₃)₃ particles agglomerating but also changes the electromagnetic parameters, thereby improving the impedance matching and attenuation ability. High electromagnetic wave absorption (EMA) was achieved by combining the 3D interconnected mesh structure and the various interfaces between NiCo₂(CO₃)₃ and RGO. The minimal reflection loss (RL_min) was −58.5 dB at 2.3 mm, and the EAB was 6.5 GHz. The excellent EMA performance of the aerogel can be attributed to the multiple reflection, scattering, and relaxation process of the porous 3D structure as well as the strong polarization of the interfacial matrix.n of the interfacial matrix.