Polymer additive are often used to reduce friction drag of wall-bounded turbulent flows.The flow with a polymer solution exhibiting viscoelastic property has been reported to reduce up to 80%frictional drag compared to that the equivalent flow of the pure solvent.This decrease in friction drag by a small amount of microscopic polymer molecules is reported to be accompanied with the appearance of thin filamentlike "shear layers" that act as interfaces separating low-momentum flow regions near the pipe wall and highmomentum flow regions closer to the centerline.However,no clear evidence correlates this shear layer to the drag reduction quantitatively.And the underlying mechanism of polymer-induced drag reduction in turbulent flow remains elusive.