Abstract: In this paper,a new method was presented to extract straight line from image based on computer vision task. Canny edge detector is used in this method to get edge, link the edge using Freeman chain code, and gradually delete no meaningful chain code to computer vision task. We use least square method to fit the straight line. The presented method can extract as much information as possible from original images. It excels both in getting the information about end points and in representing the straight line accurately.