The pumping characteristics of several types of screw elements for an intermeshing co-rotating twin screw extruder (ICoTSE) were experimentally studied using molten polystyrene (PS) as a typical non-Newtonian fluid in “LABOTEX30α”. Here, the throughput was regarded as the remainder of drag flow minus pressure flow, based on the previous theoretical and experimental studies with regard to either single or twin-screw extruders. Therefore, the relationship between the throughput and the pressure gradient for a given screw geometry was approximately expressed as a linear dimensionless relation containing two so-called pumping-characteristic parameters which depend on the element geometry and degree of departure of the used fluid from the Newtonian fluid. The pumping-characteristic parameters for two right-hand flighted screw elements (RF) with leads of 0.938D and 0.703D, a neutral kneading disk (NK) and a blister ring (BR) were experimentally determined, and the RF with a lead of 0.938D was taken as an example to observe the effect of the clearance between it and the barrel wall on its pumping-characteristic. The results show that the linear relationship between the dimensionless throughput and the dimensionless pressure gradient for each type of the screw elements used here is a good approximation, and the clearance in the range used here greatly affects the pumping characteristic of the RF. Moreover, the degree of filling and the pressure profile in two kinds of screw configurations used for water-injection foaming devolatilization, which consist of elements with different diameters but with the same dimensionless geometry as those used in this work, were predicted and discussed by using the determined pumping-characteristic parameters under the conditions of given throughput of molten PS and screw speed.