A method based on binocular vision model is discussed to determine the relative motion parameters between two space objects. The relationship between the detection of feature points and the measurement of motion parameters is studied in this instance of ignoring the camera calibrate errors. By analyzing the measurement error of center of figure of the feature point affected by image segmentation, an algorithm based on iteration of the center of the track window is used to improve the measurement accuracy. The experiment verifies that the algorithm is valid.