Abstract: The liquid-solid coupling conjugate heat transfer CFD analysis model of China Advanced Research Reactor (CARR) standard fuel assembly was set up in the paper. Through the analysis of a set of steady state flow condition, the drag characteristic curve of the fuel assembly was achieved. Based on the calculated results of the full CFD model of CARR main body under the condition of forcing flow, the natural circulation numerical simulation analysis of the standard fuel assembly was carried out. The simulation results indicate that the heat generation in the hot fuel assembly can be removed safely and the coolant nucleate boiling or flow instability will not happen under the set conditions. The temperature distributions of the coolant, the fuel cladding and the fuel meat, the hotspot’s 3D location and the natural circulation flow rate in the process of natural circulation were also obtained. The present results are valuable to provide a theoretical method and reference data for the study of transient thermal-hydraulic characteristics of the hot fuel assembly.