Abstract: Spent fuel assemblies of the sodium-cooled fast reactors are exposed to an argon atmosphere with poor heat transfer performance during the transfer process. In order to ensure that the temperature of the fuel assembly is lower than the safety limit value during the transfer process, the experimental research and numerical simulation calculation were carried out under the argon atmosphere based on the 37 rods bundle fuel assembly in the paper. The research results show that the equivalent heat conduction method can be used to simply the wire-wrapped assembly, which can meet the calculation accuracy requirements. The calculation results were compared with the experimental research results, which proves that the numerical simulation method can simulate the fuel assembly heat transfer well. In the heat transfer analysis of hexagonal fuel assembly in argon atmosphere, the radiative heat transfer has an important influence. Under the experimental conditions, the radiative heat transfer accounts for 36% to 57% of the total heat transfer.