Abstract: Numerical simulations for blunt models in hypersonic flows are carried out by solving the Reynolds averaged Navier-Stokes equation in this paper. The performances of the grid scale in the heat flux calculation are studied, and a criterion for the grid generation suitable for the heat flux calculation is proposed. It is shown that it is difficult to obtain reasonable results by using a grid either extremely fine or coarse for the heat flux calculation in practice. The grid scale adopted based on the local temperature gradient can achieve both enough space accuracy and satisfactory convergence velocity.