Abstract: Used the daily precipitation data in 45 years from 1965 to 2009, deterministic analyzed the process of heavy rain and torrential rain. Established 3 individual index and comprehensive assessment indexes that could reflected the process of heavy rain and torrential rain, and also divided the risk assessment rank. Tested the normality of the sequences of comprehensive assessment indexes about the heavy rain and torrential rain, the result showed that the heavy rain fitted the normal distribution, torrential rain fitted the normal distribution after vary, thereby determined the assessment indexes in return period of the heavy rain and torrential rain. At last, we assessed the process of heavy rain and torrential rain from 2010 to 2012 by the assessment rank and the return period assessment indexes. The result showed that, this research quantitative assessed the process of heavy rain and torrential rain in Tianshui Area timely effectively and scientific, provided support to pre prevention and reduction department, had a great meaning for increase the effectiveness and promptness of weather service