Abstract: Based on Prandtl's momentum transportation, this paper calculates in detail the physical quantities such as eddy viscosities, and ratio of eddy viscosity to motion viscosity, total stresses with respect to relative position in three regions of viscous sub-layer, buffer layer, and main turbulent stream for non-Newtonian fluid flowing turbulently in ducts, which according to Karman's three layer models and measurement of fluid parameters in evaluation apparatus, discusses the influence of polymer drag reduction on flowing properties of non-Newton fluid, analyzes quantitatively principle of turbulent reduction phenomenon and condition of increasing reduction rate.