Abstract: The shear stresses and apparent viscosities of the magnetorheological fluid (MRF) of carbonyl iron powder were measured by the rheometer under different magnetic flux densities (0-0.86 T) and different shear rates (100-1 000 s-1). The shear performance of the MRF was analyzed and the quantitative relations between shear stress and magnetic flux density were fitted. The results show that the shear stress of the MRF increased slowly but the apparent viscosity decreased exponentially with the increase of the shear rate under the same magnetic flux density. The viscosity change of the MRF coincided well with the Herschel-Bulkley model, meaning that the larger the magnetic flux density, the stronger the shear thinning effect of the MRF. When the magnetic flux densities were in the range of 0-0.23 T and 0.45-0.65 T, the shear stress and magnetic flux density showed an exponential relationship and the index value was 1.50 and 0.57 respectively. While in the range of 0.23-0.45 T, the shear stress increased linearly with the increase of magnetic flux density.