Abstract: The removable casing, as an important part of aviation engines, not only serves to protect the internal precision structure but also withstands a complex mechanical environment and thermal load. After an aero-engine had served for thousands of hours, cracks and falling blocks were found in the inner ring surface of the detachable housing during inspection of the combustion chamber casing. Macro- and micro- observation of fracture, microstructure examination, hardness testing, and energy dispersive X-ray spectroscopy analysis were carried out to figure out the cracking mode and cause. The results indicate that the cracking mode of the inner ring surface of the detachable housing is fatigue cracking. The crack originated from the artificially thinned area near the spot-welding position of the housing cavity surface, and there was rolled-in scale at the thinned area. The artificially thinned area and rolled-in scale residues destroyed material continuity and increased stress concentration, promoting crack initiation and propagation under vibration and aerodynamic loads.