Abstract: The image of drilling hole can be intuitively given by using ultrasonic detection.However,some methods which need to be used for getting the parameters from the directed image,such as playing back data of UDM100Q and measuring data from the printed drawings of some other imported instruments.An improved method,with which the edge of the drilling hole can be automatically extracted by using digital image processing of ultrasonic detection records,is proposed,and the coordinates of the edge are transformed into the coordinates of actual measurements in order to calculate the parameters such as aperture and verticality of the drilling hole.