Al-pillared montmorillonite/carbon nanocomposites were prepared by a hydrothermal method using Al-pillared montmorillonite as a template and chitosan as a carbon source, and then hot-pressed to obtain Al-pillared montmorillonite-based ceramic/carbon composites. The effect of carbon content on the densities, mechanics, electrical conductivity and wave absorption properties of the composites was investigated by X-ray diffraction, scanning electron microscopy, universal material tests and vector network analysis. The results show that the Al-pillared montmorillonite/carbon is transformed into mullite/carbon ceramic material by hot-press sintering, and the carbon is further graphitized in the hot pressing. The introduction of carbon enhances the electrical conductivity and toughness of the composites, while a large amount of interfacial polarization is formed inside the material, which enhances the dielectric loss of the composites and transforms the ceramic material from a wave-transparent body to an electromagnetic wave absorbing material. The internal microcracks of the composites increase and the flexural strength gradually decreases with the further increase of carbon mass fraction in aluminum column-supported montmorillonite. The fracture toughness of the composite material is the maximum value when the mass ratio of montmorillonite to chitosan is 32 at 1 300 ℃, 20 MPa and 120 min of holding time, which is 11.41% greater than that of ceramics without carbon addition. The maximum electrical conductivity of the composite material is 17.53 S·m-1 when the mass ratio of montmorillonite to chitosan is 4. According to the simulation calculations through wave absorption performance tests, the minimum RL value of the obtained material reaches -44.93 dB when the coating thickness is 1.4 mm. The minimum RL value is -36.28 dB and the effective absorption bandwidth is 5.0 GHz when the coating thickness is 1.6 mm.