Abstract: For heavy rainfall in western Sichuan in edge of subtropical high, as the beginning of no significant impact of the system, storm clouds generated entirely by the basin itself and the development forecasting difficult.The process can be used before the start of the regular observations and numerical forecast data on the edge of subtropical high in the two convective rainfall in Western Case were compared, analysis:This type of storm usually occurs in the prevalence of high-latitude zonal circulation, Lake Toba-Lake Baikal as a broad trough zone, middle and low latitudes as something stable and strong background to the subtropical circulation, surface pressure field is usually presented from north to south, east to the west of the distribution of low state;850hPa easterly flow of the formation of the Loop and Wudu, Hanzhong, Ankang stations and basins to maintain temperature and flow easterly mesoscale heavy rainfall conducive to the occurrence of such;500hPa north branch of the frontal zone south subtropical high pressure, and the west or north south east fall back position to the beginning of the process suitable indicating significance.In understanding the basis of such rainstorms in the background, the detailed analysis of factual information and rational combination of numerical forecast products to improve the forecasting accuracy of such rainstorms effective way.