Based on global NCEP/NCAR reanalysis data and thunderstorm data from 1979 to 2008, the relation- ships between the atmospheric heat source and the number of thunderstorm days are analyzed, as well as the variations in the number of thunderstorm days with different heat source intensities. The results indicate that the intensity of the atmospheric heat source is positively correlated with the number of thunderstorm days, with correlation coefficients as high as 0.86. Further, the correlation coefficients exceed 0.4 in eastern Nagqu, Lhasa, central Shigatse, northeastern Shannan, and northwestern Nyingchi, where thunderstorms are the most dominant activity. Further analysis shows that more thunderstorm days than the average occur in Shigatse, Lhasa, Shannan, most parts of Nagqu, and the midwestern region of Qamdo when the atmospheric heat source is stronger. In contrast, in years with a weaker heat source, the number of thunderstorm days is reduced in central Shigatse, Namling, and northwestern Nyingchi.