Abstract: LBE-cooled fast reactor (LFR) as one of the candidates of generation Ⅳ nuclear systems has the characteristics of high security. It is significance to study the thermal hydraulic characteristics under normal conditions. The commercial computational fluid dynamics software STAR-CCM+ was used to simulate the 19-bundle lead-bismuth assembly with wire-wrap by fluid-solid interaction. And it was studied on the influence of boundary conditions such as mass flow rate and total power on the internal heat transfer characteristics of the assemblies. The simulation results show that the simulation results are in good agreement with experiment results in the prediction of the temperature of sub-channel center and wall temperature. At the same time, the wire-wrap structure leads to the periodic cross mixing between the sub-channels and makes the surface temperature of rod bundle oscillate. When mass flow rate increases, the cross mixing velocity between sub-channels increases. The power change has less effect on the cross mixing between the channels, and there is no significant difference in the coolant temperature distribution.