In the prosthetic socket design, aimed at the high cost and radiation deficiency caused by CT scannming whichis a routinetechniqueto obtainthe cross-sectinaalimage ofthe residual limb, a new ultrasonic scalming method is developed to acquire the bones and skin contours of the residual limb Using a pig fore-leg as the scanning bject, an overlapping algorithm is designed to reconstruct the 2D cross-sectional image, the contours of the bone and skin are extracted using edge detection algorithm and the 3D model ofthe pig fore-leg is reconstructed by using reverse englneenng tech- nology. The results ofcheckingthe accuracy oftheimage by scanning a cylinderworkpieces show fhat the extracted contours ofthe cylinder ar。quite close to the standard circumference So it IS teasi-ble to get the contours of bones atld skin by ultxasonic scanning. The ultrasonic sCanllffig system featuring no radiation and tow COSt is a kind of new means of Cross section scanning for medical image.