N-heterocyclic carbene (NHC) polymers, characterized by abundant nitrogen sources, tunable metal centers and excellent chemical stability, serve as ideal precursors for metal-incorporated N-doped carbon materials. Herein, ligand engineering and temperature-induced strategies are employed to fabricate NHC-derived N/metal dual-doped carbon materials (CN-X-700, X = Cu, Cu/Co, and Co) with two-dimensional nanoribbon morphology. The optimized carbonization temperature endows CN-X-700 with substantial N-doping levels, numerous defects and moderate electrical conductivity. These structural advantages balance polarization and conductive losses, thereby elevating dielectric dissipation. More importantly, the Cu/Co bimetallic heterointerfaces significantly improve the electromagnetic wave (EMW) absorption capability by combining impedance matching and multiple synergistic losses, including magnetic loss, interfacial polarization and conductive loss. The comparison shows that CN-Cu/Co-700 exhibits superior loss capacity and a broad absorption range, with a minimum reflection loss (RL_min) of −62.24 dB and an effective absorption bandwidth (EAB) covering 7.11 GHz (10.53–17.64 GHz). This study reveals the intrinsic relationship between heterointerfaces, multi-loss mechanisms and EMW dissipation, providing a novel structural regulation strategy for designing high-performance carbon-based microwave absorbers.