The detection technique of small module gears has a very important research and application value. In this paper, a composite measuring method is presented based on combining traditional mechanical contact measurement with optical image non-contact measurement. First of all, this paper analyzes the basic principle of composite probe composed of optical fiber stylus and CCD imaging system. The tail-end of the stylus is shaped into a micro-sphere, where a small refection mirror is designed. When the laser is transmitted through the fiber, a round facula can be seen from the CCD camera. The micro-sphere is kept contact with the surface of the measured gear at the time of measuring and the error of the measured gear will be reflected by the offset of the facula center. Meanwhile, the sub-pixel extraction algorithm for the center of facula image is presented. Then the calibration principle and method of probe system is analyzed in detail. Finally, the data processing principle of the presented method is discussed for gear measurement.