For the low efficiency of nano-level surface finishing of Ti-6Al-4V devices, a magnetic shear thickening finishing medium is developed. Based on the processing parameters of spindle speed of 100 r/min and working gap of 0.5 mm, the influence of various abrasive particles and abrasive mass fractions on surface roughness are investigated using a designed magnetic field generator. The best processing effect was obtained when the mass fraction of the abrasive is 45%, the particle size of silicon carbide is 80 μm, and the particle size of carbonyl iron powder is 150 μm. The surface roughness of Ti-6Al-4V workpiece decreased from the initial 173 nm to 92 nm. When the particle size of silicon carbide is 30 μm, and the particle size of carbonyl iron powder is 50 μm, the surface roughness of Ti-6Al-4V workpiece decreased from the initial 170 nm to 79 nm. When the particle size of silicon carbide is 4 μm, and the particle size of carbonyl iron powder is 5 μm, the surface roughness of Ti-6Al-4V workpiece decreased from the initial 169 nm to 61 nm, and the surface roughness decreased by 64%. Under the condition of same abrasive particle size, the processing shows higher efficiency with the increase of abrasive mass fraction in the medium. With the same abrasive mass fraction, the smaller the abrasive particle size, the smaller the final surface roughness value. Scratches on the surface of the workpiece are significantly reduced, as shown bya metallographic microscope and field emission scanning electron microscope (FE-SEM), which verifies the effectiveness of the developed finishing media.