Abstract: The physical and mathematical models of the unwound screw channel of metering zone in chaos singlescrew extruder were proposed. The corresponding incompressible fluid obeyed the Carreau flow model. With the help of the mesh superposition technique provided by a polymer analysis package Polyflow, the flow and mixing of polymer melt in such an extruder, which inserted a intermittent baffle into the screw channel of metering zone, were numerically simulated. Applying the particle tracking technique and statistical methods, the mixing performance was investigated and characterized in terms of different parameters such as residence time distribution, segregation scale, mixing efficiency,and mixing index. When the baffle intermitted frequently and height slightly lower than screw channel, the chaos single-screw was better for mixing.