Abstract: Before its last overhaul, the lower roll main reducer of the piercer located in the Steel Pipe Co., Baoshan I & S Corp., Ltd.had serious vibration with the shaft and the main motor.In this case, the problem of the reducer is investigated by means of vibration measurement conducted by relevant department.Based on the actual measurement result and spectrum analysis of the reducer's vibration as well as analysis on the failure frequency elements of the bearing, the main cause for the reducer's vibration is identified, i.e., damage of the bearing.The conclusion is in compliance with that resulting from the after-dismantling-investigation of the bearing.