The work aims to seal the spent fuel transportation cask under accident conditions in order to prevent the leakage of radioactivity materials and provide basis for the sealing analysis of the spent fuel transportation through the analysis and research on sealing of scale model of the spent fuel transportation cask under the accident conditions. To verify the sealing performance of the spent fuel transportation cask under hypothetical accident conditions, the 9 m drop analysis was carried out to the scale model of the spent fuel transportation cask under accident conditions by the LS-DYNA computer program. Then, the load history of sealing bolts and the separation of sealing surface during the drop process were extracted. Meanwhile, the sealing capability test was carried out after the drop test. The results of drop analysis indicated that the stress of the sealing bolts met the limit requirements during the drop process of inner and outer covers of scale model, and the maximum separation of sealing surfaces of inner and outer covers was less than the effective rebound of sealing structure. The air tightness test conducted after the drop test showed that the sealing performance was good. According to the results of drop sealing analysis and the air tightness test of scale model of spent fuel transportation cask, the spent fuel transportation cask can meet the sealing requirements under accident conditions and the method can be used for the sealing analysis of the spent fuel transportation cask under accident conditions.