On the basis of the studies upon the computer vision system construction and the theories and technologies of the image preprocessing, the segmentation of image as well as the pixels connectivity of digital image, the methods of wiping off the noise points in the binary image of the micro plastic gears and extracting the contour of the gears were put forward. The simplifying algorithm for the contour extracting was raised by the methodology of the mathematical morphology. The principles and the implement of the key technologies of the above algorithm were also presented. It found out that a curvilinear could be represented with the fewest points by deleting the unassociated points. At last, the experiments have showed that the inspection dates of the tooth profile could be obtained accurately by the simplifying algorithm of contour optimization and the algorithm could meet the needs of the virtual engineering inspection.