A short screw extruder comprises a cylinder (1), a screw (2), and an injection shaft (3). The screw (2) comprises a screw body provided with a central through hole. The screw body comprises a left support part (2.3) and a right support part (2.4). An external screw edge (2.1) of the screw body is arranged between the left support part and the right support part. An internal screw edge (2.2) is arranged in the central hole of the screw body from a position corresponding to the right support part (2.4) in the hole. One section of the left support part (2.3) and one section of the right support part (2.4) are rotatingly matched in the cylinder (1). The injection shaft (3) is arranged in the internal screw edge (2.2). The spiral directions of the external screw edge (2.1) and the internal screw edge (2.2) are opposite. Because the external spiral channel is folded relative to the internal spiral channel, the length of screw is reduced, and thus the extruder is minimized.