The bonding of aluminum film with coated copper alumina substrate is realized by brazing technology. The new type Al/Al₂O₃ composite ceramic substrate with high thermal conductivity is successfully prepared. Mechanical polishing, chemical polishing and electrolytic polishing methods are carried out for aluminum film polishing on the surface of composite substrate. Research results show that all of these polishing methods can improve the aluminum film surface roughness and enhance the reflective rate of aluminum film. Moreover, the sample processed by chemical and electrolytic polishing method has the lowest surface roughness and highest reflective rate compared with other polishing methods.