The invention discloses an extrusion device for injection molding. The extrusion device for injection molding comprises a servo motor and a feeding cylinder. A propelling screw is arranged in the feeding cylinder and connected with the servo motor. A feeding port and a discharging port are formed in the feeding cylinder. Helical teeth are arranged on the propelling screw. The propelling screw provided with the different layers of helical teeth is used for extrusion, and the feeding effect is more ideal; a heating cylinder is additionally arranged on the outer wall of the feeding cylinder, the heating cylinder evenly transmits heat onto the cylinder wall of the feeding cylinder through a heat-conducting layer for heating temperature control, heat can be dissipated more evenly through the heat-conducting layer, raw materials in the feeding cylinder are kept in a heated state, and the situation that the feeding cylinder is blocked due to solidification of the raw materials is avoided; and the structure is simple and practical, and the service life is prolonged.