Abstract: A variable propeller bearing in a wind farm frequently cracks, which seriously affects the safe and stable operation of the unit. This paper takes a cracked propeller bearing as the research object, and studies the cause of failure through macroscopic inspection, chemical composition analysis, non-metallic inclusion analysis, mechanical performance analysis, metallographic analysis, scanning and energy spectrum analysis and other methods. The analysis results show that:（1） the minimum room temperature impact absorption energy of the propeller bearing matrix is 22.4 J,which is far lower than the standard minimum value of 35 J, which is easy to cause problems such as low fatigue resistance, poor toughness and high stress concentration sensitivity of the material;（2） The depth part of the surface hardening layer on the side of the propeller bearing is less than 1.0 mm, and the hardness of the surface hardening layer is46.7 HRC, which is lower than the standard requirements（55～62 HRC）, indicating that the processing process has failed to improve the wear resistance and fatigue resistance of the material itself;（3） There is a clear corrosion pit in the inner wall of the bolt hole of the variable propeller bearing, with a maximum depth of 0.36 mm. Therefore, it can be judged that the failure of variable propeller bearings is due to unqualified surface processing. Under the combined action of cross-variant stress and corrosion, it is easy to produce corrosion pits around the surface of the bolt hole. Fatigue damage accumulates after running in the air for a long time, further germinates multiple fatigue micro-cracks, constantly expanding along the crystal in the metal matrix, and the bearing matrix Unqualified performance promotes the expansion of fatigue cracks in its interior. Adjacent micro-cracks are gradually connected to form large fatigue cracks and continue to expand to the raceway side. When the cracks further expand to the critical size, unstable and rapid fractures will occur. In order to prevent the cracking of variable propeller bearings, suggestions are put forward such as anti-corrosion process on the surface of bolt holes, structural optimisation to reduce the intersection stress, strict control of bearing matrix manufacturing quality, and regular non-destructive testing of bearings.