Abstract: A DAC (distance-amplitude) curve for detecting the 1 mm×5 mm (depth times length) simulated crack of small diameter tube inner wall was made by using the creeping wave. If tested with a direct wave range covering the whole weld at a distance of 10-20 mm from the simulated pipe weld defects, the horizontal positioning can directly read the defect position with quantitative accuracy. When the shear wave was used and DAC curve was made through drill hole of diameter 1 mm, the reflected sound pressure for the simulated cracks (1 mm×5 mm) of both inside and outside the tube should be 7-14 dB higher than DAC curve. The experimental results show that the reflecting acoustic pressure by transverse through hole and point and planar defect has big difference, and therefore if making DAC curve by the equal depth simulated crack of small diameter tube inner wall, the quantitative errors can be avoided.