We synthesized C/Co composites via a facile one-step pyrolysis procedure and observed excellent dielectric dispersion properties at a 35 wt% filling concentration. At a thickness of 2.5 mm， the composites exhibited a minimum reflection of -23.7 dB at 11.2 GHz， with a bandwidth of 3.8 GHz （RL≤-10 dB）. To further improve their absorption performance， we optimized the macrostructure of the absorber using an all-dielectric metamaterial design. The optimized design successfully extended the less than -10 dB absorption bandwidth to 15 GHz （7.0~22.0 GHz）. Our results provide a useful reference for optimizing the preparation technology and structural design of high-performance microwave absorbers.