It　is　a　major　challenge　to　obtain　broadband　microwave　absorption　(MA)　properties　using　low　dielectric　or　magnetic　nanoparticle-decorated　carbon　composites　due　to　the　limited　single　conductive　loss　or　polarization　loss　of　the　carbon　materials　used　as　substrates.　Novel　pure　cellulose-derived　graphite　carbon　(CGC)　materials　can　be　used　as　an　exceptional　substrate　option　due　to　their　special　defective　graphitic　carbon　structure,　which　provides　both　conduction　and　polarization　loss.　Herein,　CGC@ZnO　composites　were　first　synthesized　by　atomic　layer　deposition　(ALD)　for　use　as　microwave　absorbents.　Thanks　to　the　multiple　interfaces　composed　of　graphitic　carbon,　defective　carbon,　and　polar　ZnO　molecules,　the　CGC@ZnO　composites　exhibited　superior　MA　properties.　Specifically,　the　CZ-3　achieved　a　minimum　reflection　loss　(RLmin)　of　-50.5　dB　(over　99.999%　MA)　at　6.16　GHz　in　2.98　mm.　Amazingly,　the　maximum　effective　absorption　bandwidth　(RL　＜　10　dB,　EAB(max))　could　reach　up　to　6.48　GHz　at　only　1.59　mm.　The　ultra-broadband　absorption　property　is　mainly　attributed　to　its　strong　electromagnetic　attenuation　capability　and　excellent　impedance　matching,　making　it　one　of　the　most　promising　materials　for　MA　applications.