The paper discusses the numerical modeling of starve-fed single screw extrusion of wood-polymer composites. Simulation and experimental studies on the extrusion of wood-polypropylene composite have been performed using classical three-zone screw. Using a computer model of the process, the simulation calculations of polymer plasticization, pressure and temperature profiles as well as screw filling have been carried out and validated experimentally. It was found that the screw is fully filled with the polymer only in the end part of the extruder, before the extrusion die, and the pressure is generated only in this region. The size of the fully filled region of the screw depends on the ratio of the flow rate to the screw speed. The screw filling increases with an increase in the polymer flow rate (at the constant screw speed) or with a decreasein the screw speed (at the constant flow rate). The pressure increases with increasing flow rate, and the pressure profile is well predicted.