The regulation of pore structures plays a crucial role in optimizing the electromagnetic wave absorption performance of porous materials by facilitating multiple reflection/scattering effects and improving impedance matching. Among lightweight absorbers, morphable biomass-derived porous carbon has emerged as a research hotspot due to its shape-tunable morphology, adjustable porosity, low density, cost-effectiveness, and facile fabrication. In this study, tofu was employed as a precursor to prepare sponge-like tofu and porous carbon (PCM) with varying pore sizes and densities by controlling compression pressure. The results demonstrate that moderate compression pressure induces an optimized pore architecture, which effectively enhances conductive loss, polarization loss, and synergistic multiple reflection/scattering mechanisms. The optimized PCM-4K sample achieves a minimum reflection loss (RL_min) of −41.14 dB at a matching thickness of 1.3 mm, along with the broadest effective absorption bandwidth (EAB) of 4.08 GHz at 1.4 mm. This work not only presents a novel biomass-derived carbon synthesis strategy for precise pore structure engineering but also elucidates the porous-structure-mediated absorption mechanism, providing valuable insights for the design and optimization of next-generation lightweight electromagnetic wave absorbers.