Abstract: Based on the characteristics of the reflected ultrasonic wave and through designing the block with the same curvature as the tested object, this paper aims to show the way how to ensure good coupling for the inspection. By fabricating an identifying mark for the incidence point and the refraction angle on the block, accurate and convenient measurement of incidence point and the angle of refraction can be realized by simply using the reflection of sound beam at the circular arc and large flat bottom without the need of calculation and the help of special calculation tools.