Using ten years of observation data and EC 2.5°×2.5° objective analysis data from 2000 to 2009, persistent rainstorms in northwest Guangxi in main flood period (May to August) were analyzed with the methods of statistics and synoptic climatology. The results showed that persistent rainstorms obviously occurred in the time window which mainly appeared in June and July, especially in early June. The major weather systems causing persistent rainstorm are upper trough, shear line, frontal surface, low level jet, subtropical high and tropical cyclone, etc. According to the weather system configuration, persistent rainstorms can be divided into four weather patterns, including the type of upper trough cooperating with shear line or frontal surface, the type of deep trough on the edge of subtropical high, the type of tropical cyclone, the type of middle level shear line cooperating with low level shear line. It was the type of tropical cyclone that rainfall intensity was the strongest as well as influence range was the most extensive. Based on the conceptual model analysis and ingredients method, four kinds of weather conceptual models and the specific threshold value of decision trees were established. As well as, a 24 h short term forecasting tool with forecast accuracy (TS) of persistent rainstorm in northwest Guangxi more than 10% was established by using the products of EC and T639 model.