The work aims to improve polishing rate of A-plane sapphire (1120). Non-spherical and spherical Co-doped silica sol was prepared in induction method and seed induction method, respectively. The two products were applied in chemical mechanical polishing (CMP) of A-plane sapphire. Grain size, morphology, element composition and existential state of product particles were detected with scanning electron microscope (SEM), inductive coupled plasma (ICP) and X-ray photoelectron spectroscopy (XPS). Polishing rate was verified with CP-4 polisher. Surface roughness of polished materials was tested with atomic force microscope. Chemical reaction during polishing process was analyzed based upon XPS test results of polished products. Compared with pure silica sol, non-spherical Co-doped silica sol gave 37% higher polishing rate and similar surface roughness, while spherical Co-doped silica sol had no clear advantage in polishing rate, no evidence showed that Co element was involved in chemical reaction according to XPS results. The positive role of non-spherical Co-doped silica sol in A-plane sapphire polishing is attributed to its shape priority, but not chemical reaction between Al2O3 and Co.