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With the methods of rotary EOF analysis, composition analysis, wavelet, and trend analysis， the spatialtemporal variations of thunderstorms are analyzed for 38 stations over the Xizang region from 1979 to 2008．The research results show that thunderstorms happen mainly after noon， and their durations are usually less than 20 minutes．There is quasi15year variation in the average total number of thunderstorms． Since 2000，the total number of thunderstorms has showed a more obvious decreasing tendency． The interval between the first and last thunderstorm days became shorter and shorter, but the differentia existed in different regions．The further analysis shows the interval between the first and last thunderstorm days became longer in the northwestern Changdu and the central Naqu and shorter in the other regions．