© 2015, Chinese Academy of Sciences. All right reserved. A detection system for arc surface defects of the microscope lens was proposed to improve the manufacturing quality of the lens. The image preprocessing and image edge detection were introduced the morphological operations to realize the contour extraction of a target. The image preprocessing and edge detection were added into the traditional edge detection. Then, VC ++ object-oriented programming tools were combined with the image detection for simultaneously processing the qualified lens and the defect lens to find out the faults of the defect lens. Finally, according to the results from the image processing for qualified lens and the defect lens, the difference between the qualified and the defect lenses is judged, thus the arc surface characteristic contour of the defect lens was extracted. The experimental results show that the accuracy of the designed system is 5.37 μm and the accuracy of the defect detection is 96%. The system can realize the edge extraction and edge detection of arc surface of the microscope lens.