According to the requirement of ultra-fine finishing of optical glass, composition and preparation of magnetic compound fluid (MCF) slurry are analyzed, and the polishing quality of BK7 optical glass is investigated with the different polishing parameters based on the prepared MCF slurry. Firstly, the physical performances of MCF polishing head in different mass fractions are investigated. A good shaped and stable MCF polishing head composed by iron powder 55%( mass fraction), H2O 30%, cerium oxide 12% and α-cellulose 3% is obtained. Then, the prepared MCF slurry has been used to spot polish experiment on BK7 optical glass by using a self-designed MCF polishing machine. The normal pressures of MCF polishing head and polished surface roughness have been experimentally investigated. The experimental results show that normal pressure of MCF polishing increases with the increase of spindle speed, and decreases with the increase of magnet eccentricity. And the surface roughness of workpiece has been improved from 10.2 nm to 6.7 nm after 50 min spot-polishing. It indicates that the MCF slurry meets the demand of ultra-fine finishing of optical glass.