Abstract: Porous carbon-based materials are promised to be lightweight dielectric microwave absorbents. Deeply understanding the influence of graphitization grade and porous structure on the dielectric parameters is urgently required. Herein, utilizing the low boiling point of Zn, porous N-doped carbon was fabricated by carbonization of ZIF-8 (Zn) at different temperature, and the microwave absorption performance was investigated. The porous N-doped carbon inherits the high porosity of ZIF-8 precursor. By increasing the carbonization temperature, the contents of Zn and N elements are decreased; the graphitization degree is improved; however, the specific surface area and porosity are increased first and then decreased. When the carbonization temperature is 1000°C, the porous N-doped carbon behaves enhanced microwave absorption. With an ultrathin thickness of 1.29 mm, the ideal RL reaches −50.57 dB at 16.95 GHz and the effective absorption bandwidth is 4.17 GHz. The mechanism of boosted microwave absorption is ascribed to the competition of graphitization and porosity as well as N dopants, resulting in high dielectric loss capacity and good impedance matching. The porous structure can prolong the pathways and raise the contact opportunity between microwaves and porous carbon, causing multiple scattering, interface polarization, and improved impedance matching. Besides, the N dopants can induce electron polarization and defect polarization. These results give a new insight to construct lightweight carbon-based microwave absorbents by regulating the graphitization and porosity.