The work aims to analyze and discuss the important concerns and technical requirements of nuclear criticality safety assessment during fissile material transportation, and to provide references and suggestions for the design and safety review of fissile material transportation packages. Based on the relevant evaluation standards of fissile material nuclear criticality safety, combined with some experience in the design and review of fissile material transport vessels in China, key concerns of criticality safety analysis were analyzed from the critical safety analysis model, critical safety analysis method, single package and package array. In the critical safety analysis, factors such as package size, fissile material composition, package array condition and the impact on the criticality safety of the package after the accident must be considered. At the same time, the application of burnup credit system and the loading of combustible poisons also had an important impact on the criticality safety analysis of the package. In conclusion, the uncertainty of the results obtained by the burnup credit system has a great impact on the critical safety assessment. The critical safety assessment of rods and incomplete spent fuel assemblies containing combustible poisons needs to pay special attention to the impact of combustible poisons and the impact of missing fuel assemblies.