Abstract: The connection component between the reactor pressure vessel and safety injection pipe system is an important part,which plays an important role in mitigating the consequences of a small break loss of coolant accident.Non-destructive testing for the safety injection pipe welds regularly is an important measure to ensure the stability and integrity of the safety injection pipe system The immersion ultrasonic inspection techniques for the safety injection pipe was determined though theoretical analysis and experimental research The results showed that:defect detection results agreed well with the true value of the defect,the immersion ultrasonic inspection techniques for the similar and dissimilar metal welds are able to meet the requirements of specification