The invention discloses a paper shredding machine and a paper shredding method thereof. The paper shredding machine comprises a paper passing board, a paper sucking device arranged on the paper passing board, an optical identification device, a paper shredding cutter, a control device and a paper shredding barrel for classifying broken paper, wherein the paper sucking device can suck waste paper placed on the paper passing board one by one and convey the waste paper to the paper shredding cutter along the paper passing board; the optical identification device is arranged on the part, between the paper sucking device and the paper shredding cutter, of the paper passing board, when the waste paper passes, the optical identification device is used for carrying out font position identificationon the paper surface on the front side and the back surface of the waste paper; the paper shredding cutter is arranged at the tail end of the paper passing board, and can be used for cutting the waste paper; the paper shredding barrel for classifying and storing the broken paper is arranged below the paper shredding cutter, and is used for classifying and storing the broken paper with ink and thebroken paper without ink; and the control device is used for controlling the paper shredding cutter to cut according to the font position on the waste paper recognized by the optical identification device, and therefore the ink part on the waste paper is separated from the ink-free part on the waste paper.