The optimization design of micro‐structure and composition is an important strategy to obtain high‐performance metal‐based electromagnetic (EM) wave absorption materials. In this work, ZnO/FeNi composites derived from ZnFeNi layered double hydroxides are prepared by a one‐step hydrothermal method and subsequent pyrolysis process, and can be employed as an effective alternative for high‐performance EM wave absorber. A series of ZnO/FeNi composites with different structures are obtained by varying the molar ratios of Zn2+/Fe3+/Ni2+, and the ZnO/FeNi composites with a Zn2+/Fe3+/Ni2+ molar ratio of 6:1:3 show a hierarchical flower‐like structure. Owing to the strong synergistic loss mechanism of dielectric‐magnetic components and favorable structural features, this hierarchical flower‐like ZnO/FeNi sample supplies the optimal EM wave absorption performance with the highest reflection loss of −52.08 dB and the widest effective absorption bandwidth of 6.56 GHz. The EM simulation further demonstrates that impedance matching plays a determining role in EM wave absorption performance. This work provides a new way for the fabrication of a high‐performance metal‐based EM wave absorber.