In order to meet the demand of improving the material removal rate and polishing quality of BK7 optical glass, it is proposed to improve the dispersion of the polishing fluid and prepare the polishing liquid with excellent properties by decreasing the agglomeration of the polishing fluid particles of the Magnetic Compound Fluid (MCF), improving MCF polishing performance of BK7 optical glass. Polyving Akohol (PVA), apolymer dispersant, with different mass fraction was added to MCF to analyze the particle size distribution and median particle size in the MCF polishing fluid. The effect of different amount of PVA polishing liquid on the polishing performance of BK7 optical glass was investigated. The experimental results show that when the mass fraction of PVA is 3%, the median particle size reaches the minimum of 5.854 μm, the dispersion of the MCF is the best, and the polishing performance is greatly improved. When the mass fraction of PVA is 5%, the maximum of material removal rate is 26.4×10－4g/min, and the surface roughness reached the minimum of 8.23 nm after MCF polishing 10 minutes. The addition of proper amount of PVA to the MCF, it can decrease the problem of polishing fluid particle agglomeration, improve the dispersion of the MCF, improve the Magnetic Composite Fluid polishing performance of BK7 optical glass.