Abstract: The cylindrical roller bearing of the flue gas heater in the desulfurization system of a certain coal-fired power generation unit broke. The reasons for bearing fracture were analyzed using macroscopic observation, chemical composition analysis, scanning electron microscopy analysis, metallographic examination, hardness testing. The results show that there were obvious casting defects such as looseness, inclusions and pores in the bearing retaining frame. The angle of the bearing retaining frame did not transition smoothly, resulting in stress concentration at the corner and the initiation of microcracks. As the cracks continued to propagate, the bearing retaining frame broke, which led to abnormal stress and fracture of the bearing steel ring. Improper selection of bearing lubricating oil further accelerated the fracture process of the bearing.