Abstract: The tube mouth of hot extrusion forming must be inspected by ultrasonic testing according to the “RCC-M PWR nuclear machinery design and construction rules” because of the complexity of its structure and high probability of producing multi-direction defects. The axial and circumferential artificial slot size of reference blocks for the nozzle must be fabricated according to the RCC-M specification requirement for the quality of the mother tube and according to the physical shape of nozzle. Using multi-angle probe detection, the key point was to analyze the echo from the lining of R arc contour interface, which was identified as the defect echo, verifying the feasibility of hot extrusion forming nozzle process directly.