Nanocomposites with heterogeneous structures and magneto-electric synergistic losses have broad prospects for improving electromagnetic wave (EMW) absorption performance. In this study, we synthesized Co₂NiO₄@MnCo₂O_4.5 nanoparticles with abundant hetero-interfaces and multiple magneto-electric loss mechanisms by a facile hydrothermal method. The excess 0.5 oxygen atoms in MnCo₂O_4.5 produce more vacancies and contribute to the enhancement of electrical conductivity. Sequential nanoneedle clusters facilitate multiple reflections and absorption of EMW in the materials, which are accompanied by an abundance of heterogeneous interfaces to improve the dielectric loss. The Co₂NiO₄@MnCo₂O_4.5 composites showed a minimum reflection loss (RL_min) of −30.01 dB and a superior effective absorption bandwidth (EAB) of 6.12 GHz (11.88 GHz–18 GHz) at a thickness of 2.00 mm. Computer Simulation Technology (CST) revealed that the obtained particles show very low radar cross-section (RCS) values and almost full coverage angles. The maximum reduction of RCS at vertical incidence reaches 19.98 dB m². The Co₂NiO₄@MnCo₂O_4.5 nanoparticles exhibit outstanding radar attenuation properties, which can effectively inhibit the reflection and scattering of EMW. Therefore, the prepared Co₂NiO₄@MnCo₂O_4.5 absorbers have great application potential in the field of EMW absorption.