After the optical lens is finely ground by the abrasive liquid, there is still a crack layer about 2–3m thick on the surface. The method to eliminate this crack layer is polishing. The mechanism of polishing and grinding is the same, except that the tool material used is different from the slurry. The materials used for polishing include cloth, polyurethane and pitch, which usually require high precision. For the polished surface, the most commonly used material is high-grade polished asphalt.

　　Using asphalt to polish is to drive the polishing liquid to grind the surface of the lens to generate heat through the fine surface of the asphalt, so that the glass melts and flows, melts away the rough vertices and fills in the bottom of the cracks, and gradually removes the crack layer. At present, the polishing powder used for polishing glass lenses is mainly cerium oxide (CeO2). The proportion of the polishing liquid varies according to the polishing period of the lens. Generally, a higher concentration of polishing liquid is used in the initial stage of polishing and when clamping with the polishing mold. After the lens surface is bright, use a thinner polishing solution to avoid orange peel on the mirror surface (fogging on the lens surface).

　　The movement mechanism used for polishing and grinding is the same. In addition to the different polishing tools and working fluids, the environmental conditions required for polishing are also stricter than those used for grinding. The general things to pay attention to when polishing are as follows: There should be no impurities in the surface of the polishing asphalt and the polishing liquid, otherwise it will cause scratches on the mirror surface. The polished asphalt surface must be consistent with the lens surface, otherwise it will be bounced during polishing, which will bite the polishing powder and scratch the surface of the lens.

　　Before polishing, it must be determined whether there are scratches or punctures on the surface of the lens after polishing. Whether the size and material of the polishing tool are appropriate. Whether the hardness and thickness of the asphalt are appropriate. During the polishing process, attention must be paid to the condition and accuracy of the lens surface at all times. In the inspection of lens surface defects, because the inspection process is judged by personal vision and methods, the inspector should have a deep understanding of the specifications of scratches and sand holes, and often compare the standard samples of scratches and sand holes. To ensure the correctness of the inspection.