Abstract: In order to study the influence of flow and heat transfer on the thermal hydraulic characteristics of fast reactor fuel assemblies, the Kriging method was used to study design parameters of the assemblies. The result shows that the P/D and H/D ranges change gradually in a certain direction towards the origin, when the pressure drop of the assembly increases with constant average outlet temperature. While the P/D and H/D range change is not directional when the average outlet temperature of the assembly increases with constant pressure drop. According to the calculation results, the design parameters of assemblies can be obtained under given input limit conditions, which can provide reference for the selection of fuel assemblies for larger fast reactors in the future.