An advanced expert system for supporting automatic polishing operation of mold and die has been developed. The goal of this system is to minimize the polishing time, the number of polishing and tools used. Also, this paper proposes the advanced concept of the polishing method to perform polishing operation of mold and die, and it has adapted to the orthogonal array method. as a statistical technique, to choose an optimal polishing condition. An expert system consists of the polishing machining database that includes the information of workpiece and polishing tools, and the input/output module.