due to low density, high stiffness, low thermal expansion coefficient, duplicate molding, etc., carbon fiber reinforced polymer (cfrp) is one of the potential materials of the optical mirror. the process developed for phi 300mm high precision cfrp mirror described in this paper. a placement tool used to improve laying accuracy up to +/- 0.1 degrees. a special reinforced cell structure designed to increase rigidity and thermal stability. optical replication process adopted for surface modification of the carbon fiber composite mirror blank. finally, surface accuracy rms of phi 300mm cfrp mirror is 0.22 mu m, surface roughness ra is about 2nm, and the thermal stability can achieve 13nm / degrees c from the test result. the research content is of some reference value in the infrared as well as visible light applications.