Abstract: The influences of three main parameters, i. e, the forming pressure, the heating temperature and the residence time of materials within the barrel on the working performance of the screw extruder and the quality of product, were studied.Based on Darnell and Mol' s equation, the effect of the slippage between the plug and the screw channel wall on the forming pressure build up was analysed. The study indicated that the pressure decreases with the increase of slip. The presence of slippage would reduce the maximum mass flow rate. If mass flow rate taking into account the slip is known, the pressure build up may be evaluated. The maximum axial pressure at the conveying-compacting section of the screw was measured with results very mach consistent with the theoretical evaluations. To introduce the 5-element Maxwell model, the rheological properties of agricultural waste materials compressed in a heated barrel and the pressure distribution were clarified. The residence time was determined by means of the curve of stress-relaxation. Besides, a simple method to evaluate the required quantity of thermal energy in the hot extruding process was given.