The utility model relates to a supersonic wave flaw detection contrast sample tube notch depth measuring apparatus, particularly to a contrast sample tube notch depth measuring apparatus applicable to the steel pipe supersonic wave flaw detection calibration. The supersonic wave contrast sample tube is a steel pipe with standard artificial defects. The requirement for the notch depth of the standard artificial defect is strict, with a relatively little notch width, generally being 1 mm. It is difficult to accurately measure the notch depth. According to the utility model, the indicating gauge probe is restructured into a needle-shaped probe with the diameter less than 1mm. In addition, a saddle type gauge stand is designed to form a depth measuring apparatus with the restructured indicating gauge. The notch depth can be measured by measuring the difference of chord heights of the fixed chords at the internal and external surfaces of the sample tubes.