The authors comprehensively review technique of automated optical (visual) inspection(AOI) technique from aspects of the basic principle, optical imaging method, key techniques of system integration, image processing and defect classification at the application background of automated online surface defect inspection in intelligent manufacturing industry. The key technologies of system integration in automated optical inspection, such as visual lighting, high speed imaging in a large field of view, distributed high-speed image processing, precision transmission and positioning for the inspected objects, and networked control, are briefly summarized. The basic optical principles, functions and applications of the optical imaging methods commonly used in automated optical defect inspection are comprehensively reviewed. The image processing, defect geometric feature definition, feature recognition and classification algorithm for surface defect inspection are systematically summarized. Particularly, the methods of texture background removal in the images with periodic textures, and the detect detection, recognition and classification methods for complex and random texture surface based on depth learning are reviewed.