In traditional single-screw extruder, rotating the screw and keeping the barrel fixed is often used, and the barrel usually has smooth inside wall. In this paper, we designed a single-screw extruder with a helical grooved barrel, and we let the screw and barrel rotate together in order to improve the conveying and mixing performance. Numerical simulation has been done on the co-rotating of the single screw with helical grooved barrel. In the condition that the relative speed of single screw and helically grooved barrel is 30 r/min, POLYFLOW was used to calculate the three-dimensional isothermal flow fields and mixing process of PVC-R (rigid polyvinyl chloride) in a single screw extruder at five different speeds of single screw and helically grooved barrel. The influence of different relative speeds on the mixing and extrusion performance of the single screw extruder with helically grooved barrel was investigated. Results showed that when the rotation speed of helical grooved barrel and single screw is 10 r/min and 20 r/min respectively, the mixing and extrusion performance of single screw extruder with helically grooved barrel is the best.