Abstract：To optimize the existing slurry for abrasive-free polishing (AFP) of hard disk substrate, a water-soluble free radical initiator, 2, 20-azobis [2-(2-imidazolin-2-yl) propane]  dihydrochloride (AIBI)  is introduced to the  H₂O₂-based slurry.  The polishing results show that, the material removal rate (MRR) of hard disk substrate polished with H₂O₂-based slurry containing AIBI is obviously higher than that without AIBI. The acting mechanism of the improved MRR is investigated. Electron paramagnetic resonances tests show that, by comparison with H₂O₂ slurry, H₂O₂-AIBI slurry provides higher concentration of hydroxyl radicals. Auger electron spectrometer analyses further demonstrate that the oxidation ability of H₂O₂-AIBI slurry is much greater than H₂O₂ slurry. In addition, potentiodynamic polarization tests show that the corrosion dissolution rate of hard disk substrate in H₂O₂-AIBI slurry is increased. Therefore that stronger oxidation ability and a higher corrosion dissolution rate of H₂O₂-AIBI slurry lead to higher MRR can be concluded.