Abstract: Beijing is prone to drought and flood disasters, and the special political status and the rapid development of urbanization make its flood control task more severe. In this paper, the daily precipitation data of Beijing during 1950-2017 flood seasons(June to September)are analyzed by using linear regression analysis methods, cumulative departure methods, M-K methods and P-Ⅲ frequency curve methods. The results show that:(1) There are more dry years, less continuous drought, continuous flood or alternation of drought and flood.It shows a large randomness as a whole, but it also shows the regularity of "fluctuation" intersect in some years.(2) Precipitation in the flood season is mainly concentrated in July and August.(3) The distribution of rainfall in Beijing is not uniform, which is mainly concentrated in Pinggu, Miyun, Huairou and other places in the windward zone in the front of mountains.(4) The total precipitation in the flood season shows a steady decline trend.