Magnetorheological finishing technology is a new generation of high-precision optical accessory polishing and processing methods. It presents a MRF dwell time algorithm that can quickly calculate the resident time during magnetorheological processing of the rotational optical parts. A magnetorheological forming polishing experiment on a prototype has been carried out on BK9 glass parts of 20mm rotary symmetrical face shape. The algorithm can improve the surface shape precision of the workpiece from 6.5um to 0.61um. Emulational and experimental results show that the surface shape error of a spherical polished workpiece is convergent by this method, which is also, applies to magneto-rheological finishing of non-spherical and planar workpiece.