Abstract: Component contour is often used in constructing steel structure of plant design. There are many kinds of lines in the component layout such as arc line and suspended edges which are not closed to form a loop. So, an algorithm to extract the contour with suspended edges is needed. Basic concepts and definition of suspended tree and extended contour are given, an algorithm to extract it is presented using techniques of dynamic local coordinate system and adaptive bounding box. At last, some operations related to extended contour are described.