Magnetorheological finishing (MRF) is a sub-aperture polishing process, which is often used to correct surface errors and remove sub-surface damage after grinding. A strong correlation exists between the material removal rate and surface roughness in MRF, but current theoretical models are incapable of predicting these two factors at the same time. In this paper, a theoretical model was developed to describe the material removal rate and surface quality after MRF in order to better understand the material removal mechanism of MRF and explain the relationship between surface roughness and material removal rate. Two modes of experiments (uniform polishing and fixed point polishing) were conducted on monocrystalline silicon to obtain the results of surface roughness and removal rate. The experimental results are highly consistent with the theoretical model calculated results. The theoretical model could be a reference for high-efficiency and ultra-smooth MRF process.