Abstract:The correctness of the parameters directly decides the function and performance of NC machine tools. However, it is hard to avoid the loss of the parameters, confusion or the destruction of the human factors in practical use of NC machine tools.It will inevitably lead to the failure of normal operation.In this kind of failure,it need to find out the reason and the location of the fault rapidly and accurately, and rule out the fault quickly.The article analyze the specific form and basic operation of parameters for FANUC system and flexiblly use the rich and complete self-diagnosis function of the modern numerical control system.Through specific examples,the method using self-diagnosis function to inspect, analysize and eliminate the fault related to the parameters is gived.This method does not rely on diagnostic instrument, can diagnose and treat parameter fault quickly and effectively, and can be widely used in maintenance of modern NC machine tools.