Abstract: Mullite-based ceramsite was prepared from coal gangue and bauxite. With ceramsite, ferric nitrite and glucose as raw materials, Fe/C/Mullite-based ceramics composite material was prepared by wet chemical synthesis technology combined with calcination at 900 ℃ in argon atmosphere. In the composite materials, C with a certain degree of graphitization covered the surface of the ceramsite, and Fe particles were uniformly dispersed in the grid of C layer. Due to the dielectric loss caused by the conductive polarization derived from the Fe particles and graphite, as well as the interfacial polarization derived from the interface between loading substance and matrix, the material showed enhanced absorption performance. When the ferric nitrite concentration in the initial solution was 0.1 mol/L, the sample FeCM-0.1 exhibited the best absorbing properties. The minimum reflection loss value of −13.9 dB was obtained at 14.6 GHz with a matching thickness of only 2.0 mm and the corresponding effective bandwidth was 3.6 GHz. This study provides a new way for the production of low-cost microwave absorbing materials and the resource utilization of solid waste coal gangue.