Abstract: Tight lattice rod bundles have been applied to reactors due to lts high conversion ratio.How-ever,there still exists big deficiency in understanding of the coolant flow characteristics inside the sub-channels of tight lattices.This paper investigates the turbulence air flow behavior inside both square and triangular tight lattice.The validity of both eddy viscosity models and Reynolds stress models is assessed by comparing computational results with experimental data.The results show a reasonable prediction of the nu-merical analysis using the Reynolds stress model SSG,except for the flow behavior in the gap region between the rod and the wall.The SSG model is not sensitive to the mesh structure,in the case the size of the near wall meshes satisfies y⁺＜20,while the secondary moment closure ω model shows numerical oscillation with fine mesh sizes.