Abstract: In this paper, the relation between the difference scheme and grid system is studied for solving Navier-Stokes equations with given Reynolds number. Only if this relation is satisfied in the directions x, y, z respectively, the Navier-Stokes equations can be simulated properly. In many references solving full Navier-Stokes equations with second order difference scheme, the grids in the direction z normal to the wall airs fine enough since the clustering grid technique is used. The proposed relation is satis...