The fixed-point polishing experiment of BK7 glass was carried out by using magnetic compound fluid (MCF). By building the three-dimensional model of polishing spot and simulating the spatial distribution of magnetic field, the material removal mechanism of MCF polishing was explained, and the variation of material removal rate, surface roughness and hardness with polishing time was determined. The relationship between material removal depth and magnetic flux density was established. The experimental results show that the surface profile of the polishing spot is "butterfly" shape and the cross-section profile along the axial direction of the polishing wheel is "W" shape. The material removal rate is closely related to magnetic field and polishing time, and the highest removal rate about polishing depth is 553 nm/min. The surface roughness first increases and then decreases with the increase of polishing time. The smooth surface with Ra roughness less than 6 nm can be produced by MCF polishing, and there is a positive correlation between roughness and hardness.