For wider‐band and stronger electromagnetic (EM) wave absorption, macroporous short carbon fibers/mullite matrix (Cf/Mu) composites were prepared via introducing short carbon fibers (0, 0.7, and 1.3 vol%) with length of 2‐3 mm into macroporous mullite ceramic by gel‐casting. The density of as‐prepared Cf/Mu composites decreases from 2.93 g/cm3 to 2.74 g/cm3, while the porosity increases from 3.32% to 10.76% with the rise in carbon fibers content. The diameter of macropores in Cf/Mu composites is ranging from several microns to tens of microns. Complex permittivity and dielectric loss of the prepared composites in X‐band (8.2‐12.4 GHz) are significantly enhanced with increased carbon fibers content. The best EM wave absorption performance is obtained in the macroporous Cf/Mu composites containing only 0.7 vol% carbon fibers (Cf/Mu‐0.7). The maximum absorption loss of Cf/Mu‐0.7 is −38.3 dB at 12.08 GHz at the thickness of 2.1 mm, and effective absorption bandwidth below −10 dB (over 90% of EM wave absorption) covers the whole X band with the thickness of 2.35 mm. The results suggest that the Cf/Mu composites can be promising high‐performance EM wave absorbing materials.