Abstract: In order to study the thermal and flow pattern of fuel assemblies in fast reactor, 3D simulation was performed for the 169 bundle wire-wrapped fast reactor fuel assemblies using CFD code Fluent. The result shows that when the flow rate is in the range of 10.92 to 18.67 kg/s, the relative deviation of calculated pressure drop compared with experimental results from the reference is less than 3.41%. The relative temperature of inner sub-channels rises with a fluctuation period of 1/3 of rod pitch. Local temperature of inner sub-channels can be higher than the result of sub-channel code SUPERENERGY. Based on simulation results the flow distribution and heat exchange in fuel assemblies can be more accurately determined, and it can provide reference for future thermal-hydraulic design of sub-channels.