Abstract: Due to the large blind area of the scanning surface of the ultrasonic time of flight diffraction method (TOFD), it is necessary to accurately grasp the size of the blind area before applying TOFD technology to ensure that the inspected product is effectively tested and avoid missed inspections. In addition to calculating the blind area of the scanning surface before testing, the corresponding comparison test block must also be used for verification. Combining the requirements of current detection technology, a new type of scanning surface blind zone comparison test block is designed. Using this test block, the scanning surface blind zone under different working conditions and different detection conditions can be obtained, which can avoid the deviation of the scanning surface blind zone verification. Thereby avoiding missed inspection.