It is of great importance to understand and predict screw characteristics (SC) during the single screw extrusion process for the extruder design and the operation optimization. In order to simulate SC effectively, we introduce the concept of a partial rotational fraction for a partial periodic unit of helical geometry in the metering section of the single screw extruder. In this work, the partial rotational fraction has been implemented with the finite element. We report that simple and accurate computation can be achieved at low computational cost in obtaining the three-dimensional flow field and three-dimensional screw characteristics in terms of material properties with the proposed partial period unit concept in the single screw extruder.