Taking into consideration the Extensive literature we conducted our own studies of polymer flow velocity in the helical channel of the plasticating system. They included the following subjects: studies conditions in rectangular and helical coordinate systems-a model with a rotating barrel and a model with a rotating screw (theoretical principles); computational verification on the concrete example for different screw channel depths, comparison of the models with regard to drag flow velocity, pressure flow velocity, longitudinal flow velocity (resultant), shear rate and polymer viscosity. The thesis that both models of a screw-based plasticating system with a rotating barrel or a rotating screw differ fundamentally was confirmed in the same conditions in two coordinate systems-rectangular and helical. In connection with this theoretical investigations at a rotating barrel and next their experimental verification at a rotating screw: which is a common practice, are unsuitable.