Abstract: In order to study the flow pattern of compact fuel assembly in fast reactor, three-dimensional simulation was performed to the 169-rod bundle fuel assemblies in fast reactor with Fluent code, and the results were compared with those in published papers. The results show that the calculated friction coefficient is in good agreement with experimental result when Re is in the range of 35 885 to 61 354. From central region to peripheral region, the characteristics of axial flow and cross flow in bundle vary with the direction and distance. According to the simulation result, the flow pattern in compact fuel assembly can be more accurately determined, and references for hydraulic design and flow measurement in sub-channels for compact fuel assembly can be provided.