Abstract: To overcome the deficiency of existing polishing technology, the magnetorheological (MR) polishing fluid was prepared by the abrasive and ferromagnetic composite particles, using the abrasive particles coated on the ferromagnetic particle surfaces. The morphology of the abrasive and ferromagnetic composite particles was observed by scanning electron microscopy, the rheological property of MR fluids was tested by Rheometer, and the effect of MR polishing fluid on 316L metal powder injection molding parts was verified by polishing experiment in intelligent magnetorheological polishing machine. In the results, the abrasive particles are evenly wrapped around the ferromagnetic particle surfaces. When the magnetic field is 0.8 T and the shearing rate is 100 s^-1, the shear stress reaches 45 kPa. The surface roughness of 316L metal powder injection molding parts polished by MR polishing fluid decreases significantly, showing that the magnetorheological polishing solution has the high removal rate for the surface roughness of powder metallurgy products.