Abstract: In order to reduce the mechanical vibration of fuel rods during the operation and conduce to the coolant mixing between sub-channels, the fuel assembly of lead-based research reactor was designed by using wire-wrapped fixed structure. While the wire-wrapped structure will influence the coolant flow and heat transfer characteristics inside fuel assembly, it’s essential to analyze the influence of wire-wrapped structure on the flow and convective heat transfer in the fuel assembly for optimization design of CLEAR-Ⅰ fuel assembly. In this contribution, fields of velocity, temperature and other flow field characteristics in the wire-wrapped fuel assembly were analyzed using CFD tools. The results show that wire-wraps play an important role on stirring the coolant, and the strength of stirring in inner channel is stronger than in out channel. The friction factor decreases in the entrance region and then attains periodic fluctuations in the fully developed region, and the Nusselt number changes have a same behavior. The cladding highest temperature is under the limit of safety design.