Abstract: It was found that the outer ring of the roller bearing housing was cracked after a 60-hour test run of a certain type of engine. The crack runs through the whole outer ring fitting surface of the bearing. Through the macroscopic and microscopic analysis of the fracture surface and the examination of metallographic structure and hardness, it is considered the fracture property of the bearing housing is fatigue. The cause of fatigue fracture was that it was a right-angle transition and there was obvious stress concentration. After taking measures to improve the design drawing, refine the size, improve the processing technology of the bearing housing and strength the manufacturing quality control of the parts, this kind of failure did not occur again.