Because carbonyl iron powder (CIP) has the advantages of good temperature stability, wide absorption band and strong design ability, it has been widely studied and used. In this paper, the electromagnetic wave absorption properties of two kinds of carbonyl iron powder which have the same basic parameters but different morphologies (spherical and dendritic) have been tested to study the influence of morphology on the absorption properties of carbonyl iron powder. The experimental results show that the morphology of carbonyl iron powder has a great influence on the electromagnetic wave absorption performance. Compared to the spherical CIP, the maximum reflection loss(RL) of the dendritic CIP increases by 94%, reaching -47.14 dB. Moreover, the frequencies corresponding to the minimum RL values of absorption peaks shift form 11.88 GHz (spherical CIP) to 6.44 GHz (dendritic CIP). This is because the dendritic morphology is conducive to form discontinuous network, increase the diffuse scattering of incident electromagnetic wave as well as form more interfacial charge polarization, resulting in enhancing the absorption intensity of electromagnetic wave. In addition, this study shows that the anisotropic structure is an effective way to improve the dielectric constant and dielectric loss, and obtain the absorber with the characteristics of wide absorption bandwidth and light weight.