Spent fuel storage and transportation casks have the advantages of flexibility, functional diversity, and inherent safety. In order to protect personnel and the environment, strict design standards of casks should be followed to meet relevant regulations. Thermal evaluation is an important step to determine whether the cask and spent fuel will leak or be damaged under various extreme conditions. Thermal analysis is necessary for casks under normal transportation and fire conditions to prevent the cask components and contents from overheating damage. In this paper, thermal analyses were performed on a spent fuel storage and transportation cask. The fire condition was selected to calculate the storage and transportation cask based on Computational Fluid Dynamic code ANSYS Fluent. In addition, this paper introduced in detail the assumptions and boundary conditions in the calculation, and conducted a mesh-independent analysis. The results showed that the maximum temperature of the fuel cladding was 343.6 ℃, the maximum temperature of the γ shielding layer was 243.4 ℃. The maximum temperature of spent fuel and various parts of the cask were below the temperature limit. The calculation results meet the requirements of relevant regulations and could provide reference for design.