A rotary printing machine includes a printing cylinder, at least one clamping unit mounted on a printing surface of the printing cylinder, and a feeding control mechanism and an unloading control mechanism mounted to a lateral side of the printing cylinder for changing the clamping state of the clamping unit. When the clamping unit is moved to an unloading position, the unloading control mechanism can be operated to control the clamping unit to maintain a closed state, so that a workpiece can be brought by the printing cylinder to a feeding position again. Then, the feeding control mechanism can be operated to control the clamping unit at the feeding position to maintain a clamped state, so that printing can be repeated on the workpiece to form multiple layers of ink and create three-dimensional printed layers showing a specific visual effect.