An auto paper-combing mechanism of a paper shredder has a frame formed with a feeding channel and a fixing shaft, and a feeding salver. A plurality of combing needle beds are disposed on the fixing shaft; a combing needle is inserted in the bottom of each combing needle bed. The needlepoint of each combing needle heads toward the outlet of the feeding channel, and the height of combing needles are in a ladder-like distribution. The vertical distances between the needlepoint of each combing needle and the lower edge of the outlet of the feeding channel are equal.