The transport cask for spent fuel assemblies undertakes functions such as preventing criticality, containment, shielding, and removing decay heat. In order to better analyze the thermal conductivity of the neutron shielding layer of the spent fuel transport cask, the work aims to study the effective thermal conductivity of the neutron shielding layer for a certain type of spent fuel transport casks. The 3D computational fluid dynamics software was used, the effects of different heat transfer fins on the axial and radial effective thermal conductivity of the neutron shielding layer and the temperature of the inner ring surface under normal transportation and accident conditions were studied. The results showed that using heat transfer fins with bigger thermal conductivity could effectively increase the thermal conductivity of the neutron shielding layer. For axial and radial thermal conductivity, when using copper fins, the effective thermal conductivity was about 6 times that of using carbon steel fins and 10-13 times that of using 304 stainless steel fins. Due to the small inner diameter of the transportation cask studied in this paper, the effective thermal conductivity calculated by the area weighted mean method was higher than that of the numerical calculation method, with an error of about 17%. The average temperature differences of inner surfaces of the shielding layer with different heat transfer fins were not significant after 30 min fire. The result has a strong guiding significance for the design of spent fuel casks and the thermal safety analysis.