The RCF life of bearing balls is a main method to evaluate the performance of bearing materials and their production technology. In general, the RCF life of ceramic balls is a reliable technique to asses whether or not they are suitable to be used in rolling bearings. The rolling contact fatigue test has practical characteristic. The long time, noise heavy make the tester tired. The fault occurring, the chain reaction is generated. The test rig destruction is strong unless quick treatment. The characteristic frequency of test rig rotating member is calculated. The fault is diagnosed by characteristic frequency. The test indicated that the fault diagnosis accurate, effective and feasible.