Abstract: This paper consists of four parts. First, the requirement of fidelity and its assessment indicator for numerical results with high order accurate methods, meshes, physical models and high performance computer are investigated. Second, the problems in large eddy simulation and direct numerical simulation with high performance computer are discussed. Third, the relation between numerical scheme and mesh is analyzed for solving Navier-Stokes equations with given high Reynolds number. Finally, a new method for verification and validation of CFD simulation is proposed.