This article proposes a novel extruder based on converging-diverging flow for polymer processing. The extruder is composed of four vane plasticizing and conveying units (VPCU) and three mixing units. The working principle of the new extruder is described in detail. Film was produced on this machine by using of CaCO3 filled LDPE composites. The film's mechanical properties were studied in terms of tensile strength and tear strength. The microstructure of the composites was studied in terms of SEM. The thermo-mechanical history of the material suffered in this extruder can be remarkably shortened in contrast to a single screw extruder with the same maximum output. Experimental results showed that the die pressure has little effect on output. More CaCO3 can be filled into the blend without degrading the parts performance.