The shape control of micro-nano-scale ferromagnetic metal particles leads to anisotropy and surface atomic ratio change, and has a great influence on its electromagnetic properties. In this work, micron-sized metallic cobalt particles with divergent branching structure were prepared by one-step hydrothermal reduction. Through the design of the composition of the reaction system, the size of the branch structure was controlled. According to the difference of the aspect ratio of the branches, sisal-like, flower-like and spheroidal particles were obtained. Themorphology and structure of the materials were characterized by SEM, TEM and XRD. The room temperature magnetic properties and electromagnetic parameters of the materials were tested by VSM and vector network analyzer. The microwave electromagnetic properties of the material in the 2-18 GHz band were studied. The results show that cobalt particles with moderate branching structure (flower shape) had the best loss capacity of electromagnetic wave, based on the increase of surface atomic ratio and coercivity caused by shape anisotropy, as well as the multiple scattering effect of multi-scale petal structure on incident electromagnetic wave. The study also found that, on the one hand, the hierarchical structure could promote multiple reflection and scattering of electromagnetic waves through a richer interface and multi-scale synergy, there by prolonging the transmission path and enhancing microwave dissipation. On the other hand, excessively branched structures could lead to improving the conductivity and dielectric loss of the absorbing composite, which was not conducive to the increase of the amount of absorbent added and the impedance matching design [ABSTRACT FROM AUTHOR]