Magneto rheological (MR) fluids are a new kind of smart vibration mitigation material for vibration control, whose shear yield stress can change in magnetic field. The rheological properties, anti-settlement stability are the very important properties of MR fluids. In this paper, a kind of preparation process of MR fluids is introduced and MR fluids with different concentrations of carbonyl iron particles along with suitable additives are synthesized. Then the properties of self-prepared MR fluids are tested, including the sedimentation stability test and viscosity test. The results of the MR fluid property tests show that the adding of 10 micrometer sized carbonyl iron particles will improve the sedimentation rate of MR fluids.