A paper breaking device for a printing machine comprises a paper breaking cutter, a connecting base, a cutter shaft, a driving part and a cutter box. The paper breaking cutter is installed on the connecting base, and the connecting base is connected with the cutter shaft and can drive the paper breaking cutter to rotate along with the cutter shaft under the effect of the driving part; when in a non-paper-breaking state, the paper breaking cutter is pushed into the cutter box to be hidden under the effect of the driving part, and the cutter box is located on one side of a paper feeding belt on the printing machine. The paper breaking device for the printing machine has the advantages of being simple and compact in structure, simple and convenient to operate, good in safety, high in reliability and the like.