• Hierarchical ZnO microspheres were successfully synthesized via spray-annealing strategy. • Pure dielectric loss ZnO materials were assembled by nanorods and nanoparticles with adjusting different aspect ratios, defects and polar faces. • Hierarchical ZnO-1 materials shown the widest efficient absorption region from 9.9 to 18.0 GHz at 2.4 mm. Regulating orientation growth plays a dominant role in enhancing dielectric properties for the electromagnetic (EM) functional materials, which faces a huge challenge in the synthesis method. By spray-annealing strategy, hierarchical ZnO microspheres assembled by ZnO nanorods and nanoparticles were successfully fabricated. With confined microsphere space and controlling crystal growth, oriented ZnO nanorods possess rich defects, Zn-polar, O-polar faces, and high permittivity. Meanwhile, temperature-dependency of exposed polarization surfaces is discovered in the semiconductor ZnO nanoparticles with evolved aspect ratios. As pure dielectric EM wave absorption material, the hierarchical ZnO microsphere exhibits adjustable complex permittivity and polarization behaviors. When the thickness is 2.4 mm, the hierarchical ZnO-1 absorber shows the widest efficient absorption (RL ≤ –10 dB) region from 9.9 to 18.0 GHz (8.1 GHz, ∼50.6% testing frequency). The minimum reflection loss (RL) of ZnO-1 can reach –31.5 dB at only 2.0 mm. Because of the outstanding dielectric loss ability and wide absorption frequency, large-scale hierarchical ZnO microspheres can be a potential EM absorption candidate.