The work aims to conduct thermal analysis on the pressurized water reactor 24P spent fuel transport cask to ensure that its design meets the requirements of safety analysis, so as to provide a reasonable time window for its transportation operation. Computational fluid dynamics software was used to conduct 3D thermal analysis of the spent fuel transport cask under loading conditions, normal transportation conditions, and accident conditions. The highest temperature of each parts and the boiling time of the water inside the cask under different operating conditions were obtained as a function of decay heat and initial temperature of the pool, which provided a basis for determining the loading operation time window of the spent fuel assemblies. According to the analysis results, after using nitrogen drainage, the highest temperature of the spent fuel assemblies reached 400 ℃ after vacuum drying for about 34.37 hours. If the vacuum drying could not be completed due to abnormal conditions, the helium backfilling operation must be completed before this time window to ensure that assembly temperature was within the safe limit. Under normal transportation and accident conditions the temperature of the main parts of the cask was within the safe temperature limit. Under accident conditions, the temperature of the spent fuel assemblies reached its maximum value of 379.7 ℃ approximately 22 hours after the accident, meeting regulatory requirements. The analysis in this paper provides reference for the thermal analysis and loading operations of spent fuel transport casks in the future.