Abstract: Experiments on magnetorheological finishing (MRF) were carried out to remove the subsurface defect (SSD) layer left by conventional polishing. The simulation and experiment results show that, the scanning interval of MRF will lead to the mid-spatial frequency error of corresponding frequency, the instability of the polishing spot will leave the mid-spatial frequency error of uncertain frequency, and an approximately linear correlation is found between the depth of removal and the peak value of power spectral density (PSD) of processed components. With MRF as the method to remove the SSD layer, the quality of processed components concerning the mid-spatial frequency is greatly affected by the processing settings. If a thick SSD layer is left by an inappropriate prior polishing, the PSD after MRF will exceed the limit.