Abstract: The feasibility of U shape notch replacing V shape notch in the reference block for ultrasonic testing of zirconium tube applied in Candu reactor was analyzed in theory. Using the ultrasonic testing equipment Rota 25 to detect the echo from the U shape notch and V shape notch separately, the obtained echo amplitude was analyzed. The result showed it was reasonable to use U shape notch to replace V shape notch in test blocks for ultrasonic testing of zirconium tube applied in Candu reactor.