The utility model discloses a square paper tube cutting machine. The cutting machine mainly comprises a machine tool main body (1), a square mold core (2), linear stretching tool rests (4) for clamping blades and a demold mechanism (5). The linear stretching tool rests are adopted to cut a square paper tube which is tensioned by the built-in mold core and ensure the intact cut, cutting edges need to cut from the outside to the inside according to a mold core jacking scope, and the cutting force which exceeds the built-in mold core jacking scope is continuously applied so as to become an overturning force and form a tearing effect. More than two tool rests (4) are needed to oppositely cut the square mold core (2) in parallel by double edges along an opposite direction, and are directionally arranged to form a cut-off tool group.