Abstract: Biomass-derived carbon has garnered significant attention in the field of microwave absorption due to its intricate natural structure and environmentally friendly attributes. In this study, a straightforward and sustainable carbonization method was utilized to synthesize composites, employing metal-precursor-impregnated sugarcane fibers as the starting material. The microwave absorption characteristics of these composites were subsequently examined. Owing to the synergistic interaction between the dielectric loss properties of the biomass carbon and the magnetic loss contributions of the NiFe components, along with optimized impedance matching and enhanced attenuation capacity upon compounding, the NiFe/SDC composites demonstrate superior microwave absorption performance. The most effective sample in this investigation achieves a minimum reflection loss of −48.86 dB at a thickness of 1.4 mm, with a maximum effective absorption bandwidth of 5.46 GHz at a matching thickness of 1.7 mm. This high-performance absorber fulfills the criteria of being lightweight, highly absorptive, broadband, and easy to process, offering a practical pathway for the large-scale fabrication of electromagnetic wave absorbers from abundant natural plant waste.