The Ω type weld detecting system applied to test Ω type weld which connects drive mechanism of reactor control bar with the top grail seat of reactor is made up of ultrasonic test subsystem, eddy test subsystem, and visual test subsystem. Localization part is one important part of the detecting system. It included a protrudable and retracted mechanism, a motor, and a protecting circuit. The successful developing of the localization part is in favor of the Ω type weld detecting system to locate precisely and automatically.