Material removal mechanism in MRF process by nano-sized diamond abrasives is proved to be a plastic shear removal. Process experiments showed the relationship between polishing parameters (rotation speed, gap between polishing wheel and work piece, and intensity of magnetic field) and peak removal rate or surface roughness. Polishing spot is proved to be stable and repeatable. Within 2.5h, the change of peak removal rate is below ±0.3% and the change of volume removal rate is below ±0.5%. One HIP SiC flat (202mm in diameter) is polished with KDMRF-1000F polishing machine and KDMRW-3 water-based MR fluids. After rough polish (30h) and finishing polish (9h), its surface form accuracy peak-to-valley (PV) is 0.13um, root-mean-square (RMS) is 0.012um and roughness RMS is 2.439nm.