Abstract The fixed agglomerated diamond abrasive pad had been used to planarize ultra-hard and brittle materials such as sapphire and SiC. However, the processing stability and surface integrity of sapphire remain to be improved. A silica-assisted fixed agglomerated diamond abrasive polishing (SA-FADAP) process was developed to solve the above mentioned problems. The material removal mechanism of the SA-FADAP was explored by analyzing material removal rate gradient (MRRG), surface topography of workpieces, the pad abrasion, and wear debris in the slurry wastes. The effects of silica grains on the self-conditioning processes of fixed agglomerated diamond abrasive pads were discussed. The efficient and stable SA-FADAP was mainly realized by the chemical-mechanical interaction produced by agglomerated diamond abrasives and silica polishing slurry.