Abstract: A certain type of aero-engine was disassembled and inspected after 2 081 h of total running time. Two cracks along the blade longitudinal distribution were found on a TC6 titanium alloy high pressure compressor stage VI rotor blade. The causes of cracks were analyzed by means of macro observation, fracture analysis, metallographic examination, energy spectrum analysis and hardness test. The results show that the cracks were fatigue cracks produced during the test run. After the engine was disassembled and inspected after the stage test run, the clearance between the blade tip and the casing seal coating does not meet the design requirements, resulted in serious friction between the blade tip and the casing seal coating during the subsequent test run. It caused local over-temperature and block falling, formed fatigue crack source and finally expanded into cracks.