Abstract: Developing high-performance electromagnetic interference (EMI) shielding materials is critical for addressing the increasingly complex electromagnetic environment. Herein, flexible, symmetric sandwich-structured POE-CNTs/EPDM/Fe₃O₄ composites were fabricated via layer-by-layer assembly followed by hot-pressing. By adopting an absorption-reflection-absorption hierarchical architecture, initial surface reflection of incident electromagnetic waves was effectively suppressed while multiple internal reflections and absorptions were enhanced, significantly boosting absorption capacity and overall shielding performance. The composite achieves a maximum EMI shielding effectiveness of 40.69 dB and an absorption coefficient of 0.45 in the X-band. Introducing a porous structure into the central reflection layer further elevates α to 0.57, confirming an absorption-dominated shielding mechanism. Notably, the material exhibits exceptional flexibility (elongation at break: 665%), thermal stability, and chemical resistance. After 500 bending cycles, prolonged thermal aging, or immersion in strong acid/alkali solutions, it retains over 90% of its initial SE, demonstrating outstanding durability. This work provides a simple, low-cost strategy for designing flexible EMI shielding materials, promising for applications in outdoor, high-temperature, and other harsh environments.