Abstract: According to the existing development methods and experience of fault diagnosis expert system, this system uses rule-based knowledge representation and reasoning mechanisms. It's specified to the specific CNC roll grinder features. Kinds of diagnosis information of numerical control machine are stored in factbase and knowledge database. Decision tree is used to simulate the reasoning process. This rule-based fault diagnosis expert system of numerical control machine can make the correct diagnosis of most common faults.

Key words: numerical control machine, expert system, rule, fault diagnosis