The purpose of this paper is to develop a robust and efficient high order fully conservative finite difference scheme for compressible Navier-Stokes equations. The 5th order WENO scheme is used for the inviscid fluxes. A conservative fourth order accuracy finite central differencing scheme is developed for the viscous terms. An improved ε value of 10-2 is suggested for the WENO smooth factors calculation, which removes the weight oscillation and significantly improves the convergence rate and level. The wall surface is taken as half-point mesh so that the no slip wall boundary condition can be accurately imposed. A 3th order accurate finite difference scheme is given to treat wall boundary condition. The implicit time marching method with unfactored Gauss-Seidel line relaxation is used with the high order scheme to achieve steady state solutions with high convergence rate.