Daily precipitation data collected in 38 weather stations in the Tibet plateau from 1961 to 2007 are used to analyze the spatial and temporal variation of precipitation events in rainy season, including the rain day in different grades and intensity, and its influence on drought and flood. The main conclusions are summarized as follows. The rain day and the light rain events increased in North Tibet and decreased in South Tibet, but the moderate rain events increased in the lower reaches of Yarlung Zangbo River to eastern Qamdo. The rain days in rainy season had a decreasing trend in recent 47 years, mostly due to the significant descent of light rain day and the decreasing of contribution of light rain to precipitation, but the moderate rain day and its contribution increased. The precipitation intensity showed an increasing trend due to the increasing of the intensity of light rain and heavy rain. The events of light rain were frequent before 1980s, the events of moderate and heavy were frequent during 1980-2000, the events of light rain were frequent during 2001-2007. The contributions of heavy rain had an obviously positive trend in 1990s. The extremity brought drought and flood which were likely to become severe due to the change trend.