Magnetoelectric composites can achieve magneto-electric synergy to optimize impedance matching. However, it is challenging to enhance the broadband absorption performance for thin thickness absorbers. Herein, FeNi₃@C composite with magnetic alloy core and N-doped macroporous multilevel layered carbon shell was constructed by hierarchical interface engineering. The uniform multilevel layered carbon shell could induce interfacial polarization and multiple scattering, and further endows enhanced electromagnetic attenuation and optimized impedance matching. An ultra-thin broadband absorber with an effective absorption bandwidth of 7.4 GHz is achieved at a thickness of only 1.6 mm. Moreover, full-band absorption from 2 to 18 GHz at a thickness of 9.8 mm is realized through metastructure design. This work provides an alternative strategy to prepare core–shell structured magnetoelectric composites for ultra-thin and broadband absorbers.