The invention discloses an ultra-precision processing method for a sapphire substrate based on a fixed abrasive polishing pad, which mainly includes three steps of rough grinding, fine grinding and polishing: first, a W75 nickel-plated diamond fixed abrasive grinding polishing pad ( FAP) to roughly grind the cut sapphire blank, secondly, use W28 nickel-plated diamond FAP to fine-grind the rough-grinded workpiece, and finally, use W5 diamond FAP to polish the fine-grinded workpiece, that is, to complete the grinding and polishing process. The invention processes the sapphire substrate, shortens the whole process to less than 2 hours, greatly shortens the processing time of sapphire, and finally can obtain the sapphire substrate with the workpiece surface roughness Ra less than 3nm, and can effectively remove pitting, scratches and other surface defects , and the subsurface damage is low, and the surface quality is excellent. The invention improves the processing efficiency and surface quality of the sapphire substrate, and has low cost and no pollution.