As the most important ore mineral in various tin deposits,cassiterite plays an important role in direct dating of tin mineralization and revealing ore genesis through the study of its UPb/PbPb geochronology. In this paper, the diffusion parameters of Pb in cassiterite were calculated,and the closure of UPb isotopic system in the term of diffusion dynamics was discussed. In addition,the retention of Pb isotope information in cassiterite under different temperatures was also discussed.The results reveal that the closure temperatures of UPb in this mineral are relatively high, and its UPb isotope system could be easily kept closed under most geological conditions in various tin deposits. Compared with other isotope systems commonly used as geochronometers, original UPb isotope information in cassiterite should not be easily lost by diffusion. This conclusion obtained in this paper provides an important theoretical basis for the reliability of cassiterite UPb dating, and will further promote the development of geochronology on hydrothermal deposits in China.