Polymer devolatilization, including flash, surface renewal and stripping-agent-added techniques in screw extruders, is one of the most important polymer processing technologies. Its development requires an understanding of the relationships among some facts and subjects. Surface renewal devolatilization (SRDV) is a commonly used technique, which includes the two essential elements of film interface area and exposure time. A main feature of SRDV in various types of screw extruders is extrusion devolatilization, in which those elements vary with screw speed and throughput. An extrusion-devolatilization model for SRDV model has been developed, which solves some important engineering problems encountered in devolatilization.