Abstract: Taking Dunhuang fresco as the research background, we design a fresco-oriented line drawing extraction algorithm combining with the fresco-specific background knowledge and artistic style in this paper. L0 image norm is used to remove the unimportant details, and an improved FDo G operator is posed to extract the image contour. Based on our line drawing extraction algorithm, we further design and develop a fresco-oriented computer aided copying system which provides the functions such as layer management, mural contour extraction, murals copying, and so on. The results and the evaluation show that even users who do not have basic painting skills can copy better. The system can not only bring much fun for users, but also can protect Dunhuang＇s fresco.