Abstract: Based on the principle of ultrasonic TOFD technique for the detection, location and sizing of defects, the side drilled holes and notches in a 2.25Cr1Mo steel block of 110 mm in thickness were inspected using a multi-channel TOFD inspection system. The D scan and A scan images of defects were given .The corresponding relationship between D scan and A scan image was also analyzed. The errors of defects location and size were no more than 5%. The result validated the good measurement accuracy of ultrasonic TOFD testing. Thus, criterion was provided efficiently for evaluation of natural defect images examined by ultrasonic TOFD equipment on site.