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PDCs-SiCN(Co) were composed by polymer-derived technique from polysilazane and Co nano-powder. XRD, SEM and hysteresis loops patterns show that there are magnetic Co nanoparticles and newly formed magnetic Co3C particles in the compound, which makes the composite possess the required impedance matching due to the combination of dielectric and magnetic properties, thus having certain microwave absorption properties. Electromagnetic wave absorbing performance of the PDCs-SiCN (Co) ceramics was discussed when the frequency range is 2-18GHz. PDCs-SiCN (Co) ceramics mixed with 5wt% of Co nanoparticles provides best electromagnetic wave absorption performance compared with other Co contained samples when the thickness is 2mm. The minimum RL is -8.3 dB at 16.7 GHz, this means that 85% of the incident electromagnetic waves enter the material at this frequency and are further depleted. The minimum reflection loss (RL) of all samples was decreased and its corresponding frequency was also changed with the increase of sample thickness. Bandwidth of microwave absorptivity exceeding 88% (RL< -9 dB) of sample which doped with 5wt% cobalt reaches 0.35 GHz when the thickness is 7mm. The results indicated that the prepared materials have certain microwave absorption properties and have potential application prospects in the field of microwave absorbing materials.