The invention relates to a banknote quality detection system and a method based on deformation restoration technology. In the banknote quality detection, the employed algorithm reserves main characteristics of image data of a training set and common changes, data irrelevance in the training set is removed, a real-time image is reconstructed, related data portions in the training set in the image are reserved, irrelevant portions in the image are removed, the real-time image and the reconstructed image are compared point to point to obtain a difference image, and defects are detected after thresholding. According to the system and the method, problem of inaccurate layering of offsetting and intaglio areas in a positioning process by the conventional method is solved, offsetting and intaglio do not need to be distinguished in a detection process, geometric distortion can be tolerated, and offsetting and intaglio boundaries and positions which simultaneously belong to the neighborhood of the offsetting and intaglio areas and are difficult to be located and detected are detected. According to the system and the method, the detection precision is improved, the detection false alarms are reduced, a machine can be reminded to rapidly and accurately discover problems, and the product quality is effectively controlled in time.