Letterpress printing refers to the graphic part of the printing plate is higher than the non-graphic part, the ink on the ink roll can only be transferred to the graphic part of the printing plate, and the non-graphic part is no ink, so as to complete the printing of the printed matter. All printed paper back with slight impression convex, line or dot edge part neat, and printing ink in the center part of the light, is relief printing. In contrast to relief printing, the graphic portion of the plate is lower than the non-graphic portion, forming a groove. The ink is only covered in the groove, there is no ink on the surface of the plate, the paper is covered on the upper part of the plate, and the plate and the paper are pressed to transfer the ink from the concave part of the plate to the paper.