Worm cars are widely used for the processing of polymer systems and composite materials with complex rheological behavior. To describe the flow of recyclable media using different rheological models. Widespread mathematical flow models based on the use of models Ostwald – de Waele (grade model). This is due to its relative simplicity, clarity and ease of determination of rheological parameters. Meanwhile, the lack of known power-law model: inflated viscosity at low strain rates. Therefore, the mathematical model of flows, based on a power model should give inaccurate forecasts in determining the integral parameters. In this paper, error estimation model Ostwald – de Waele made by comparing the calculated results with the results obtained using the “standard” model, which was used as a rheological model three-parameter Ellis. Ellis model well describes the rheological behavior of polymer solutions and melts in the field of small and medium strain rates. To our knowledge, such assessments for the considered flow was carried out. The flow of the generalized Newtonian fluid between the two parallel flat walls (unfolding worm), of which one is at rest, and the other moves in its own plane with a constant velocity. The distance between the walls (the depth of the screw cutting) is constant. The flow is laminar, steady, isothermal. Wednesday incompressible. Inertial mass and strength compared to viscous friction forces are negligible. Slipping on missing surfaces. The work includes the general solution of Couette flow of generalized Newtonian fluid, obtaining computational formulas for models Ostwald – de Waele and Ellis, a comparison of the calculated results of the solutions. The analysis of the results shows that power law model causes significant errors at relatively low speeds wall motion.