Abstract: Evaluating the transfer function,thedynamic relation between the pressure in the die and the speed of the screwis necessary to studythe pressure close-loop control svstem in a single screw extrud-er.The transfer function ofasingle screwextruder was evaluated via mechanism analysis. It showec that thetransfer function of single screw extruders is a proportional component by the experiment testing method.Using theresultsand thetransfer functions of other components in the close-loop control sys tem，amathematical model in theclose-loop control system of the extruder could be formulated.

Key words: single screw extruder;transfer function, mechanism analysis;experiment testing, pressure close-loop control system