The characteristics of magnetorheological finishing (MRF) technique such as the behavior of magnetic particles and the magnetic field distribution have been investigated. Based on the established theoretical model, material removal function and removal rate experiments involving a K9 glass mirror are designed and carried out. Further experiments are carried out to improve the surface roughness of the workpiece. The final surface roughness with an initial value of 17.58 nm reached 0.4351 nm rms after 35 min of deterministic MRF, and the AFM measurements on microstructures of the polished surface are also improved by 0.445 nm rms without obvious defects.