Electromagnetic absorption materials have drawn increasing attention owing to their wide applications in military, aerospace, communication and the electronic industry. Efficient microwave absorption with tunable bandwidth and thermal stability is a great challenge. Herein, we fabricate a novel 3D hierarchical Co3O4-rGO hybrid-architecture by a facile, green and highly tunable strategy. The porous Co3O4 flower is assembled uniformly, introducing great amount of interfaces. Tailoring Co3O4 flowers could improve interfacial polarization and dipole polarization as well as conductive network, highly tuning the hybrid-architectures and electromagnetic properties. The reflection loss (RL) reaches -61 dB at Co3O4/rGO ratio of 2: 1, as well as frequencyselective absorption. Furthermore, the RL are relatively stable and the bandwidth is broadened almost covering the whole investigated frequency at elevated temperature of 353-473 K. The result is ascribed to utilizing multi-interface magnetic micro-flowers to tune impedance matching, which is accompanied with strong relaxation loss and electrical loss, as well as magnetic loss. Our work confirms that 3D hierarchical Co3O4-rGO hybrids as a potential candidate for high-efficiency microwave absorbers in harsh environment, and provide a novel pathway for designing microwave absorber in the future.