Magnetorheological finishing (MRF) is a novel precision optical machining technology. MRF utilizes magnetic particles, nonmagnetic polishing abrasives in carrier fluid, and a magnetic field to finish optical materials. Owing to its flexible finishing process, MRF eliminates subsurface damage, corrects surface figure errors and the finishing process can be easily controlled by computer. To achieve deterministic finishing, it’s necessary to know the mechanism of material removal. Different magnetorheological fluids are used to finish optical glass on the same machining condition. The material removal and surface quality are examined after finishing with no polishing abrasive, aluminium oxide and cerium oxide. The results show that the hardness of polishing abrasive is not the main factors to affect material removal.