The present invention provides a method for accurately extracting that profile error of cycloidal gear and rapidly analyzing the key shape and position accuracy. By means of variable magnification measurement, the use of a combination of panoramic and accurately measured fields of view, the detection path planning of the tooth profile and the position precision of the mounting hole of the cycloidal gear are reailzed, the extraction of the outline of the mounting hole, the accurate establishment of the workpiece coordinate system, the extraction of the tooth profile outline in turn according tothe detection path are completed, and each outline coordinate point through image data processing is obtained, thereby obtaining the tooth profile error of the cycloidal gear and the position error of the mounting hole.