In this article, the aggregation behavior and shear properties of magnetorheological fluid (MRF) under different magnetic field strengths, volume fraction of magnetic particles (MPs) and shear rates were investigated by coarse-grained molecular dynamics simulations. With the formation of a wall-like structure, the shear stress (tau) of the MRF increased linearly in the shear strains region 0 < strain (gamma) < 0.58. In the yield region (gamma > 0.58), the stress began to decrease and finally tended to be stable. The relationship between the aggregation of MPs and shear stress under a magnetic field-shear field was determined at the microscopic level.