A classical optical processing method for a class of lightweight silicon carbide mirrors is presented. In the fine grinding stage, the mirror body is subjected to fine grinding experiments with emery and boron carbide respectively. Results show that under the same fine grinding time, the grinding amount of the boron carbide granular abrasive (240#) is at least 0.01 mm larger than that of the emery granular abrasive, and the cutting effect is obviously better than that of the emery granular abrasive, the best process parameters for fine grinding is with a load of 50 N and a spindle speed of 45 r/min. In the polishing stage, using the asphalt polishing mold as the base, the mirror body is polished with cerium oxide polishing liquid and diamond liquid respectively. Results show that the diamond liquid can effectively improve the surface shape and surface quality of the parts. And the optimal process parameters for polishing is with a load of 30 N and a spindle speed of 60 r/min. The mirror body is polished with diamond liquid with two particle sizes of W1 and W0.3 respectively, which can make the mirror body surface best reach 3 low apertures, the surface finish is good, and there are no obvious paths and bright spots. Due to the particularity of the structure of the mirror body, it is difficult to polish the mirror body. A ring polishing machine is used to polish the mirror body without stress and modify the local irregularity of the mirror body. The irregularity of the final part can meet one aperture.