Critical precipitation is an important indicator for forecasting mountain torrents. According to the features of mountain torrents in Jiangxi Province, the relation between precipitation, occurrence time of mountain torrents, and basin parameters has been studied. The results indicate that precipitation and torrents have a close relation. The correlation between precipitation and basin parameters is considerable. Critical precipitation amounts within 1 h, 3 h, 6 h and 24 h were calculated in the 11 small basins by using mountain torrents and meteorological data of these small basins during 1950 to 2002. A statistical model concerning critical precipitation, basin area, main river length, and main river slope has been built. Moreover, the critical precipitation amounts for the other 1045 small basins have been calculated by using the model. The tests have indicated that the model has good effect in the application to a typical mountain torrent event in Ganzhou City during 2-3 July 2009.