Abstract: It is of significance to detect and measure the height of cracks in order to assess the life of nuclear power equipment. In this paper, the measurements of the height of surface breaking defects by conventional UT tip diffraction method and TOFD method were compared. The conclusion was drawn:for breaking defect of height being less than 4mm, the resolution of conventional UT tip diffraction method decreases sharply; using TOFD with A scan can distinguish breaking defect of height greater than 1mm. With the increase of breaking defect height, two methods of measuring results are basically identical.