Gansu is a province with frequent rainstorm. This paper gives a brief introduction to the natural geographic situation which closely relates to rainstorms. Based on long term rain monitoring data from rain stations in Gansu and statistics on long term average periodic maximum rainstorm for 5 time intervals known as 10 min, 60 min, 6 h, 24 h and 3 d, the 3 representative rivers of Heihe, Zulihe and Taohe were selected to study the rainstorm change law of 5 time intervals along with different elevations, which is useful to understand rainstorm change law along with elevations, rainstorm characteristics of Gansu Province as well as to instruct rainstorm observation and water resources calculation in mountainous areas.