Abstract: Cracks were produced prematurely in the transition area of the shoulder root of TC4 alloy fan rotor blade of an aero-engine. The cause of the cracks was studied through macromorphology observation, fracture analysis and contact discharge test. The results show that the cracks of the failed fan rotor blades were fatigue cracks, and initiated on the surface of the transition area from the root of the leaf pot side shoulder to the exhaust edge. The induction coil closed or contacted the blade substrate and contact discharge occurred, resulting in local melting and burning of the blade substrate and melting of the flow blocking agent during the brazing process of the wear-resistant layer of the blade shoulder, which was the cause of fatigue crack initiation of the blade. It was suggested that insulating the induction coil by insulating tape and using an appropriate induction current and welding distance to prevent contact discharge between the coil and the blade.