Abstract: Numerical simulations were performed on developed turbulent flow through reactor fuel assembly in equilateral triangle lattice, and impacts of different turbulence models built-in computational fluid dynamics upon simulation results of flow field in channels with complicated geometry were analyzed. The results show that simulation result greatly depends on the choice of turbulence model. Due to the complicated geometrical construction, the complicated three-dimensional turbulent flow shows highly anisotropic characteristics. Turbulence models assuming isotropic turbulent viscosity fail to predict secondary flow phenomena during turbulent flow in fuel assembly channel. By solving Reynolds stresses transport equations, the more elaborate turbulence model, Reynolds stress model (RSM) can catch secondary flow accurately. The present studies provide valuable references and guidelines for further investigation on convective heat transfer simulation in complicated geometry and thermal hydraulic analysis of reactor core.