The flow and heat transfer characteristics of the fuel assembly components in the core are different at different Reynolds numbers, where the resistance to flow and the location of the highest temperature are crucial for the safety analysis of the core. In order to study the flow heat transfer characteristics of the core components in each state in detail, the FLUENT software was used to conduct a three-dimensional numerical analysis of the 169 rod-beam fast reactor fuel assembly. The results show that the error in the transition zone from laminar to turbulent flow is the largest, so more detailed treatment is needed. The flow resistance of the fuel assembly increases with the increase of Reynolds number, and the flow resistance is the largest in the rod-beam region, which is 70% larger after stabilization. With the increase of the Beckley number, the heat transfer capacity of the fuel assembly increases, and the high temperature region inside the rod bundle region of the fuel assembly is always concentrated in the center region of the fuel assembly, showing a distribution of high center temperature and low edge temperature. At the same time, the temperature distribution is correlated with the velocity.