The invention discloses a plastic extruder which comprises a cylinder and a screw rod arranged in the cylinder. An extruding channel is formed between the outer wall of the screw rod and the inner wall of the cylinder. A feeding port, an exhaust port, a discharging port and a dirt discharging opening are sequentially formed in the cylinder along the extruding channel. The plastic extruder further comprises a filtering part. The filtering part is connected to the connecting position of the discharging port and the extruding channel. By means of the plastic extruder, in the flowing direction of the extruding channel, the discharging port is located in the upstream part of the dirt discharging opening, impurities and plastic particles which are not melted are filtered out of the discharging port through a filtering part, due to the fact that the dirt discharging opening is located in the downstream part of the discharging port, discharging cannot be affected by dirt discharging, and the discharging port can achieve continuous discharging.