Abstract: A light pen based binocular stereo vision measurement system for largescale workpiece was developed,in which feature points extraction and matching technology were studied deeply. The sub pixel edge of ellipse spot was achieved accurately by the algorithm based on Canny operator and Zernike moments. Based on the ellipse spot edge points, the curve fitting method based on the least square was used to realize the center extraction of the ellipse spot. Aiming at the matching problem of feature points,the matching method based on position constraint was proposed.Experiment results demonstrate that the proposed method can extract the sub pixel edge of the ellipse spot, accurately calculate the center coordinate of the ellipse spot, and the matching rate is greater than 95%.