Abstract: The control rod guide split pin is a key connecting part of the nuclear power plant reactor internals. Stress corrosion cracking is an important potential danger that affects the quality of the split pin after long-term operation. In order to achieve an efficient and accurate inspection of the control rod guide split pin, a multi-chip integrated card-shaped ultrasonic probe is designed in this paper, and a system suitable for automatic underwater non-destructive testing is established. The results show that the split pin inspection system is with high detection efficiency and task adaptability, which provides a basis for field application inspection.