Abstract: After the factory test run of an aero-engine, it was found that the spherical washer of the aero-engine cracked. The cracking reason of the spherical washer was analyzed by means of macroscopic observation, fracture analysis, energy spectrum analysis, metallographic examination and hardness test. The results show that after the cyanidation treatment, the grinding temperature was too high, resulting in grinding burns, forming a black ball-shaped area. After rapid cooling, there was a large residual stress in the area, resulting in grinding cracks, which eventually led to the cracking of the spherical washer.