Based on the analysis of hourly rainfall in 200 mountain torrent disaster cases and the water-levels and runoff of 15 examples,it is found that the rainfall distributions in mountain torrent disasters generally can be divided into three kinds: mono-apex,bi-apex and multi-apex.The majority were the mono-apex.Mesoscale system activities are found in all of the cases.In mono-apex cases,rains are mostly local,and the heavy rains are transitory.While in bi-apex examples,rains are mainly systematic,and the heavy rain lasts for a longer time.In multi-apex cases,rains are durative,and heavy rains goes on for a long time.The key factor that triggers mountain torrents is the 6-hour rainfall intensity in most cases.