Abstract: Cracks occured at the corners of the aircraft accessories suspension casing of an aeroengine. By means of macroscopic observation, fracture analysis, stress analysis and finite element simulation analysis, the causes of cracks in the aircraft accessories suspension casing were analyzed. The results show that the cracks were fatigue cracks with large initial stress. When the aircraft accessories suspension casing was assembled with the fan casing, the process of knocking the locating pin into the pin hole would lead to local deformation of the aircraft accessories suspension casing, thus forming a large initial stress at the crack location. Under the vibration working environment, the aircraft accessories suspension casing would produce cracks and expand. This kind of problem could be avoided by ensuring that the mounting side assembly dimensions of the fan casing and the aircraft accessories suspension casing were clearance fit, and using process screws to fix the aircraft accessories suspension casing before assembling the positioning pin.