Abstract: In this study,Qujiang river basin in Sichuan was chosen as the research area to reveal the main reasons which lead to the high frequency floods since the 21st century.The spatial-temporal distribution and short-period heavy precipitation characteristics were analyzed by using the hourly precipitation data of 1970-2012.The results indicate that:1) The distribution of precipitation,rainstorm days and coefficient of variation in northen area turns out to be larger than it in southern area in Qujiang basin;increasing extremely trends of precipitation had been found in northern area in recent years.2) The short-period heavy precipitation occured in northern area a lot and increased recent years.It is also find that it usually happens during 4-8am 3) During the latest 43 years,the maximum hourly rainfall intensity of most area in Qujiang basin has increased,especially in northern area where hourly rainfall intensity is always greater than it in southern area.Therefore,the changing trends of heavy precipitation over Qujiang basin is one of the essential reasons which causes floods frequently in this area.