Mathematical morphology takes image morphological characteristics as the research object, its image processing algorithms are dilation operation, erosion operation, opening operation and closing operation. It is applied in image preprocessing such as image enhancement, image segmentation and noise filtering, etc. A wide-ranging and in-depth research is made on domestic and international applications of mathematical morphology in online printing quality detection and a variety of new automated printing quality testing equipments are developed. The direction of future research on the printing quality online detection is mainly about establishment of the standard of printing quality of motion image capture detection, application of gray image algorithm in color image processing, classification of color defects, the reduction of calculated amount and improvement in instantaneity in the image preprocessing, etc.