Abstract: The main failure modes of traction electric drive system are the fracture between rotor guide bar and end ring(short circuit ring). This paper analyzed the short circuit ring's welding process at first, and then, designed the inspection technology of the failure area based on the ultrasonic phased array detection method; meanwhile, the reliability and applicability of the UT testing were verified through the simulation and the reference block test methods. This paper provided some new ideas for the design of test technology for common failure detection of moving car motor.