Abstract: ased on the parabolized Navier-Stokes equations,a law of drag coefficient is found by the perturbational analysis of PLK type which is exactly equivalent to that based on the complete Navier-Stokes equations,as far as the problem of an incompressible laminar flow past a finite flat plate at zero incidenee is coneerned. The fact that this law is valid for flows with Reynolds number down to 15 illustrates the adaptability of the parabolized Navier-Stokes equa-tions to viscous flows with moderately low Reynolds number.

Key words: Navier-Stokes equaiton, flat plates, simplification