Abstract: In order to investigate the mechanism of the effect of orientation magnetic field on dynamic viscoelasticity of cobalt particles filled magnetorheological elastomer (MRE), cobalt particles were synthesized by a solvothermal method. The XRD and SEM results indicate the spherical cobalt particles have close-packed hexagonal structure with particle size within the range of 1-2 μm. Silicone rubber was used as the matrix to prepare cobalt particles filled MRE. During the curing process, different orientation fields (0 mT, 480 mT and 1 154 mT) were applied to prepare different MRE, and their dynamic viscoelasticity were tested. The results indicate the ordered structure formed by the cobalt particles was enhanced with increasing orientation field. As a result, the storage modulus G ' and the loss modulus G ″ of Co particles filled(MRE) increase with increasing orientation field. However, when the orientation field exceeds a critical value, the ordered becomes stable, and the effect of orientation field on dynamic viscoelasticity of MREs becomes insignificant.