The invention discloses an extruder. The extruder comprises a hopper; multiple brackets for erecting screen plates are arranged on the inner wall of the hopper; the brackets are slidingly connected tothe inner wall of the hopper; connecting blocks are fixedly arranged on the inner wall of the hopper under the brackets; working springs are fixed at the bottoms of the brackets; the ends, far from the brackets, of the working springs are fixedly connected with the connecting blocks; and lifting devices for controlling the brackets to slide up and down in the hopper are arranged at the bottom ofthe connecting blocks. The extruder can filter impurities in materials, guarantees the extrusion molding quality of the materials, prevents the wear of screws, extrusion cylinders and the like, and can control screen plates to achieve a bounce effect in a working state to prevent the materials from accumulating on the surfaces of the screen plates and to enable the materials to smoothly enter a machine cylinder through the screen plates.